Sheffield Hallam MP, Jared O’Mara, has announced he will be taking time out to deal with his mental health after his former aide accused him of being “the most disgustingly morally bankrupt person I have ever had the displeasure of working with”.

In a statement on his website, the independent MP apologised to his friends, family and constituents, saying: “I have not been honest with you about the depths of my depression and self-loathing.”

O’Mara said his thoughts had become “incoherent to the point where most recently I suffered a delusional episode”. But he made no promises to stand down, despite constituents and former staff members urging him to do so.

The MP made the announcement as a woman who worked in his office went public to accuse him of waging a persistent campaign of sexual harassment that had left her feeling “intimidated and degraded”.

The 20-year-old told the Times that O’Mara sent her inappropriate messages, often late at night or early in the morning, in which he repeatedly declared his feelings for her and commented on her appearance.

She claims that he also regularly made “sexist, misogynistic and lewd comments” about other women including female politicians, creating an “increasingly toxic” environment in his office.

O’Mara admitted telling the woman he was in love with her but that he made the declaration during his delusional episode.

“The messages I said were not of a sober or rational mind and felt like an out of body experience when I sent them, but I know that does not excuse my actions because I should not have been self-medicating with a drink to get into that state. It was my lowest point and I will be apologising personally to her and her family,” he said.

But Jacob Millen-Bamford, who worked for O’Mara for almost two years after he confounded expectations by beating the then-Liberal Democrat leader Nick Clegg in Sheffield Hallam in June 2017, said the MP should stand down.

“I am disgusted and appalled by the atrocious sexual harassment Jared is in the news for today. He should face the consequences of his actions and he should resign. He does not deserve the privilege of representing Hallam. I am ashamed to have worked for him. I hope the victim is getting all the support she needs through this dreadful time. It is completely unacceptable that she has had suffer this awful behaviour,” Millen-Bamford said.

Gareth Arnold, O’Mara’s most recent communications chief, resigned using the MP’s own Twitter account on Tuesday night, accusing him of failing his constituents and being “selfish” and “degenerate”. Yet by Thursday afternoon O’Mara appeared to have forgiven him, saying in his statement: “To my dear, old friend – the Noel to my Liam – Gareth: Thank you for sticking with me like I am sticking with you.”

O’Mara was selected to stand as a Labour MP in the snap general election of June 2017 by Labour’s national executive committee, bypassing local party members.

By October 2017, he had been suspended over a string of homophobic and misogynistic tweets he had written before his election. In July 2018, he quit the party to stand as an independent and has accused Labour – and particularly Jeremy Corbyn – of bullying him.

But Labour insisted the party had offered O’Mara support. A spokesman said: “We take the welfare of our MPs very seriously and, while Jared is no longer a Labour MP, we are concerned for his welfare and we have continued to provide support to him, and will continue to do so.”