Carly Simon somehow appears both brittle and unbreakable as she opens the door to her hotel room in Boston, Massachusetts, where a publicist hovers discreetly. She is wearing a blue sweater, blue jeans and a blue scarf and is smiling broadly. Her hair is shoulder length with the familiar low fringe. She puts on a pair of glasses; lukewarm hotel tea is ordered and poured.

The singer-songwriter is chatty and charming. She says she has just been listening to the audio version of her latest memoir, Touched by the Sun, about her friendship with Jackie Kennedy Onassis, the widow of former president John F Kennedy and the Greek shipping magnate Aristotle Onassis. It is read by Elizabeth McGovern, who plays the Countess of Grantham in Downton Abbey. That is fine with Simon, a fan of British TV, including Downton and Last Tango in Halifax.

Simon was described as a “feminist icon” on the book jacket of her 2015 memoir Boys in the Trees, a bible of A-list gossip. The daughter of Andrea Heinemann Simon, a civil rights activist, and Richard Simon, co-founder of the book publisher Simon & Schuster, she found singing an effective way to overcome a childhood stutter, recorded more than a dozen Top 40 hits and offered lyrics that stuck in the cultural consciousness.

She had romantic liaisons with Warren Beatty, Mick Jagger, Kris Kristofferson, Jack Nicholson and Cat Stevens, and an ill-fated marriage to James Taylor. Now, at 74, if anyone has earned the right to casually drop names and use terms such as “lover” without affectation, it is her.

Carly Simon with Warren Beatty in 1984. Photograph: Paul R Benoit/AP

Both her memoirs are searingly frank. When she was seven, Simon was sexually exploited by a 16-year-old boy. An abusive relationship continued until she was about 14. “I think it’s changed me for ever and there was nobody around who could possibly have believed the stories I would have told,” she says.

“It was just an awful thing to have happened. Do I think it would have happened now? The awareness of it might have prevented it. I don’t know that for sure, but also I’ve been abused in other ways and by some of the same people that Ronan Farrow talks about in his book.”

Farrow, an investigative journalist and friend of Simon, has just published Catch and Kill, about his quest to uncover numerous sexual assault allegations against Harvey Weinstein. Simon alleges that she, too, was abused by the disgraced Hollywood producer – not sexually, but in other humiliating ways.

“He asked me to score a movie that his wife at the time had made, a little Japanese cartoon, and so I did it in good faith,” she recalls. “I hired musicians and scored the movie and, at the recording session, I said: ‘Well, how shall I get paid?’ He said: ‘Well, we’ll figure it out later,’ and he never followed up.”

There was another incident at Camp David, the US presidential country retreat, the weekend before Bill Clinton’s impeachment hearings. Weinstein brought his film Paris, Texas for a screening attended by the president, first lady Hillary Clinton and guests including Simon.

“At the end of it, Harvey had the nerve to get this cheap guitar from somewhere and bring it to me in the theatre seat and say: ‘Sing now. Sing Anticipation.’ The guitar was out of tune and one of the strings was off it. So he embarrassed me greatly. I couldn’t not do it because everybody turned around to look at me in the theatre and there I was.”

How did Weinstein get away with so much for so long? “Well, people obviously were so intimidated by his power and wanted to be on the receiving end of what one maybe thought of as largesse, that maybe there was goodwill behind all of his seduction. I can just see him in all the scenes that are painted of him with the women. I was lucky not to be one of them.”

Simon and James Taylor, to whom she was married for 10 years. Photograph: Richard E Aaron/Redferns

But the way in which Weinstein, and others, took advantage of her still rankles: “I think that stealing from one financially may be one step below [doing so] sexually. I wrote about it for this book: I wrote about the various experiences that I’ve just talked to you about, and my editors, all of whom are men, said: ‘No, don’t write about that.’ I don’t blame them for that. It was just that you’re not supposed to talk about it.

“Maybe the time will come when we women who have been raped financially will be on the record to talk about that because I know a lot of other women who have been screwed. A lot of men have been screwed, too. There aren’t as many of them as men who are in powerful positions to do it, but I’m sure that it’s probably being done by women as we speak.” She adds mischievously: “I can see 10 of them right now seducing young boys, saying that they’ll pay them.”

And yet she has gnawing doubts about the #MeToo movement. “I welcome it and now I hope that it will go back to a position where things will be normalised,” she says. “Not that I want anybody to shut up or to not tell it like it is, but it also feels a little bit unnatural for me that men can’t say a flattering thing to a woman without there being a possible reckoning.

“I’m a woman and I’ve been subject to that and there was the casting couch in a number of cases in my life that I was harmed by. But I think at this point it’s just dangerous for men to act like men. Not that the men who go overboard and disrespect a woman are acting like men. You know what I mean.”

As has become clear by now, a conversation with Simon is an exercise in six degrees of separation. On Bill Clinton, she says: “When he’s interested in a subject and he’s talking about it to a woman, there’s a different energy that comes across. He has ‘the glint’ and he can’t help himself. It’s charisma. His face changes. He doesn’t look the same. His energy comes through the expressions of his mouth and his eyes. He lights up a room with his energy.”

Yet even as Hillary Clinton continues to speak out, Bill is conspicuously absent from the 2020 Democratic primary campaign, effectively banished to exile in the #MeToo era. Simon is dismayed at the thought. “That’s so sad because, to me, he’s a tremendous asset and he’s such a charismatic and brilliant, brilliant man, and whatever lesson he had to learn, he learned it.

“It was of a particular time where there was a hairline of a difference between then and now. He didn’t do himself proud, but that’s passed, that’s over with, and now let his brilliance shine through.”

Her view of Trump is rather different. She met him once in New York at a luncheon for Benazir Bhutto, the late prime minister of Pakistan, and was left cold by his overtures. “When I came into the room, there was Trump and a whole bunch of New York dignitaries. Trump wasn’t paying any attention to me at all. Why would he?

“Benazir Bhutto summoned me and asked me to go into the bedroom with her and so I went and we sat on the bed and she held my hands and said: ‘I just love your music.’ We talked about different songs that were her favourites and it maybe lasted three minutes.

“When I went out of the bedroom, obviously I had all of a sudden become important through the eyes of Donald Trump. So he was very anxious to meet me and invited me to Mar-a-Lago [his luxury estate in Florida] and was all over me like ugly on an ape.”

She turned down the offer, she says, “because I thought he was kind of repulsive”.

Simon with Bill Clinton in 2003: “He has ‘the glint’ and he can’t help himself.” Photograph: Steve Granitz/WireImage

Simon’s greatest hit, You’re So Vain, seems spookily apt for Trump. Simon agrees. “He is so vain, that’s for sure, and not in the best possible way. He doesn’t bring humour to the word. In the song, hopefully, the person could wink at himself in the mirror because he got the joke.

“I don’t think there’s much interest outside himself. What will happen with a narcissist is that they’re interested in themselves and anything that’s an extension of themselves, perhaps their children, but he’s not interested in the philosophy of great thinkers. I suspect.”

Thrice-married Trump has boasted about groping women, and been accused of sexual harassment, and of making a hush-money payment to the adult film star Stormy Daniels. What would Kennedy Onassis, whom Simon befriended in 1983 and whose own first husband was a notorious philanderer, have made of him?

“I think she would have been astounded that he could have risen to the position that he rose to. And some of the things he did and said would have been fodder for her amusement and probably disdain.”

Simon would call Kennedy regularly from rehab while dealing with anxiety and depression, which have haunted her as long as she can remember. She starting taking Prozac in 1989 to help her deal with a fear of flying and nerves when she was up for an award at the Oscars; fortunately, her category was up first, and she won, for the Working Girl theme song Let the River Run (she also sang Nobody Does It Better for the 1977 James Bond film The Spy Who Loved Me).

But Simon continued taking medication, including those not necessarily prescribed for depression, but which “changed my consciousness”. She admits now: “I have a special interest in pills. They have a certain effect on me in the same way that little candies would. If I want to change my consciousness, especially if I have a terrible headache, there’s something very promising about taking a pill. I developed a relationship with them as if there was something more secretive about it than there really is. Now I take pills in front of people or not in front of people.”

When recovering from breast cancer, she took the opioid OxyContin for about two years but, unlike millions of Americans, did not become addicted. There have been other drugs. “Is cocaine readily being done still, I wonder? I’ve done it four times, on my gums, and I loved it. I thought I was so wonderful. It made me feel confident. It made me lose all of my self-consciousness. I just thought: ‘My God, I’m not worried about how I’m coming across.’ I was actually recording, but it wasn’t on stage.”

Simon has seen a radical shift in attitudes towards drugs during her lifetime. She is adamant: “They should all be legalised. It makes it much more attractive to the wrong people if it’s not legal. It makes the price soar. If prohibition hadn’t happened, it wouldn’t have created some of the alcoholics.”

Alcoholism played a part in the breakdown in 1983 of her decade-long marriage to Taylor, she says. “I was too young. I think we were both too young to understand what the disease of alcoholism was like. He was blinded by the force of the alcohol and the other drugs he was high on.

“I didn’t know how to deal with it. If I had been stronger, I would have done. I tried so many different things and I was wrong about at least half of them. I was wrong about saying you can never do that again or it doesn’t matter, I’ll do it with you. Every turn I took seemed to be the wrong turn, but I tried really hard and so did he. He really tried hard.”

The couple had two children, Sally and Ben (“John Lennon was our nextdoor neighbour and the first person that gave us a gift after Ben was born”) and “inspired each other artistically”, she recalls. But she and Taylor have not spoken for years. “That’s one of the sad things in my life. He just doesn’t want to have any contact with me at all. I don’t know what he says about it in interviews. I think he just avoids the question.

Simon with her friend Jackie Onassis in 1989. Photograph: Stephen Rose/Getty Images

“I listen to some of my songs now as if through James’s ears and I don’t like them because I think: ‘Oh my God, what was I thinking? What would James have thought?’ I listen to his music, especially the older music of his. I just hear it on the radio all the time and it always makes me happy. It’s wistful, but happy because I love his music so much. I love him.”

After Taylor, Simon was married to the writer James Hart for 19 years – they divorced in 2007 and he came out as gay. She has been in a relationship with Richard Koehler, a surgeon, for nearly 14 years.

“Monogamy is a very hard thing,” she says. “Very hard. I think there’s always an attraction to novelty … It’s more of a man’s problem. I’ve never known a man who wasn’t attracted to the adventure of seeing whether he could get a woman to be interested in him.”

It is a sentiment that evokes Simon’s most famous lyric, “You’re so vain/You probably think this song is about you.” How did she come to write it? “It was at a party that my sister and I were giving because I was living with my older sister at the time and somebody walked into the party. And I thought: ‘Wow, he’s so vain.’”

Since the song’s release in 1972, the identity of the vain man has been the subject of intense speculation. “I have told a number of people,” she says cryptically. Simon has previously declared that the second verse was about Beatty. But now she qualifies: “Maybe. I was forced to say something.”

Before she travels back home to Martha’s Vineyard, an affluent island off Cape Cod, she wonders whether the same lyric would have generated such intrigue if written by someone else. “I don’t know whether it was me at that time in the universe with the men that I was with. It certainly is fascinating that it would be so interesting. God, I should think of some more provocative titles!”

• Simon’s memoir, Touched by the Sun, published by Little, Brown, is out now, price £20. To order a copy for £17.60, go to guardianbookshop.com. Free UK p&p on orders of more than £15, online only.