There’s a joke in my family that I joined Facebook to spy on my children, and they befriended me because they knew I wouldn’t bother. I’ve never been one to snoop on my nearest and dearest, and have always avoided writing about them, but two events this week have prompted a temporary change of heart.

In Tuesday’s books podcast, we marked LGBT history month by interviewing Christine Burns, a campaigner for transgender rights, about her history of the UK’s trans community. The next day, my son was in a TV documentary – deep breath – about polyamory.

I’d known for a while that Love Unlimited was coming but was not sure I wanted to see it. And since I live in London, and it was only broadcast in Scotland, there was every opportunity not to. There I might have left it, had it not been for the subtitle of Burns’s Trans Britain, which collects the sometimes bleak experience of trans people over half a century into 22 essays.

The news that my husband and I would be living in separate cities prompted a colleague to squeal: 'But who’s going to do his washing?'

The subtitle is Our Journey from the Shadows, and its point is that, in order to be understood, people first have to be seen. In the podcast studio, after the recording, Burns launched into a good-natured rant. Wouldn’t it be refreshing, she said, if just once an interview on trans issues didn’t have to start back at square one, explaining the terminology and addressing all the popular fallacies: “We’re always repeating the same answers to the same basic questions that have been asked since at least 1958.”

Love Unlimited wasn’t about trans people, but about life choices that challenged traditional thinking about relationships. The Oxford English Dictionary traces the word polyamory back to 1992 and says it is not to be confused with casual recreational sex, serial monogamy or swinging. My 24-year-old son was one of a dozen or so young people – gay, straight, bisexual, trans and cis – interviewed about love lives that to them seem entirely normal, but which all involve the possibility of committed partnerships with multiple lovers.

The interviewees included three gay men, two of whom work as nurses, who are filmed whiling away an evening with board games in their Edinburgh flat before retiring to their two bedrooms (there isn’t room for all three to sleep comfortably in one bed, and shift work means often only two of them are in anyway). Their setup is known in polyamorous circles as a triad or “thruple”. What, they say, could be more ordinary?

My son’s arrangement is a daisy chain, in which each person is free to have other lovers while remaining committed to each other. He currently has only one partner, but “they” – the pronoun of choice – are also in a lesbian relationship, so I resonate strongly with the splendidly upfront mother of one of the gay nurses as she recalled her initial reaction to the introduction of a third partner: “[I thought] that’s my baby’s man … Does this mean they’re not going to get married? Is my baby going to be lying in bed alone at night crying because his partner’s not there and is away shagging some other bloke?”

But that maternal worry isn’t going to disappear because I try not to think about it. The film says my son and his partner regard themselves as non-binary “in that they identify as neither exclusively masculine nor feminine”. Wrong, says my son, when I discuss it with him: they see themselves as neither exclusively male nor female, but his partner strongly identifies as femme.

Such delicate distinctions can wrongfoot the best of us. Pronouns, in particular, have been an issue in my household since my son came out as trans. I am clumsy in my attempts to negotiate a way around “he” and “they”. Childhood anecdotes in particular frequently leave me blundering back to “she”. I am amused by their description of each other as “beaux”, as the word transports me to my teenage infatuation with the Regency romances of Georgette Heyer.

There’s nothing new about being conceptually moored to our own pasts. Back in the 1980s, my father was horrified that I was not planning to change my name after getting married, while the news that my husband and I would be living in separate cities prompted a colleague in south Wales, where I was a trainee reporter, to squeal: “But who’s going to do his washing?”

To them, my relationship seemed as bizarre and dangerous as my son’s undoubtedly does to many people today – yet it turned out to be if not “the” then at least “a” new normal. While Trans Britain valuably documents the long history behind what can seem to be a new phenomenon, Love Unlimited points to a paradigm shift among some millennials that is clearly enabling them to flourish. There’s even a very chatty Dundee polyamory group, which meets up once a month over coffee and cake to debate “poly” posers such as how to deal with envy and jealousy.

What, the interviewees were repeatedly asked, were the main challenges of their lifestyle. Trust, they said – and timetabling. I for one feel greatly reassured. There will still be board games in the evenings.

• Claire Armitstead is associate editor, culture for the Guardian