I was 12 when Love Actually came out. In the eyes of my younger self it was a great film – vignettes of love I could only imagine one day feeling, all coloured by the fairy lights of Christmas. And there was even a cameo from Mr Bean himself, Rowan Atkinson. The film captured the romance I craved as a preteen, the idea that maybe a kid I fancied in my class would learn the drums for me and run through airport security to ask me out.

I was young enough to think it was sweet for Keira Knightley’s husband’s best friend to turn up on her doorstep declaring his quite obviously unrequited love. I even thought it was adorable that he ruined their wedding video by filming only closeups of her face. Of course, I feel differently now about problematic moments like these – even if I do have the film to thank for introducing me to Joni Mitchell.

I’d be happy to never watch it again, but there’s one scene that has always stuck with me and that is when Emma Thompson ’s character finds out her husband (Alan Rickman) is having an affair. She discovers a gift-wrapped necklace in his coat pocket and assumes it will be her Christmas present. Instead, when she opens it, she finds a  CD of Joni Mitchell’s Both Sides Now , and the realisation that he has given the jewellery to another woman. She goes upstairs, puts the album on, and we watch for a few tense minutes as the weight of betrayal and deceit hangs over her. She stands alone in her room only allowing herself a moment to cry silently before she heads back downstairs to her family.

It moved me when I first watched it as a 12-year-old, not even really understanding what her husband had done. But there was something in her performance. The silence of it. How she tries desperately to control her emotions in a way that, even as a preteen, I could somehow understand.

As I went back to that film for the next few Christmases, I continued to be struck by Thompson’s performance in this small narrative, how much power you can hold by holding back. But also, just how sad she looked. It was this sadness that made me think to myself: if I ever find myself in that situation, I’ll leave. Watching it one Christmas as a teenager, I made a little promise to myself that I’d choose to end a relationship rather than stay and live with that pain. Surely it would be better to finish things than be treated this way.

Some years later I was in a long-term relationship. Our agreement had been monogamy, and like most relationships it was fun and good from the start, but it soon became quite obvious that things weren’t right. I see now that I was suffocated and sad for most of it, yet I had been manipulated into believing that my unhappiness was my own doing. I was unable to feel that I deserved better, so I stayed.

But one spring morning I found myself sitting in our living room, listening as he admitted to an achingly long series of betrayals. We’d had an argument that had somehow led to this admission that he’d been cheating throughout the relationship. I’d been completely blindsided.

I looked around at this small life we’d built together – the messy bookshelves, the guitars hanging on the wall – and only saw the lies that had been its foundations. He wanted me to forgive him and for us to move on, and he genuinely believed I would.

But later that day as I sat alone in the bedroom, that scene from Love Actually popped into my mind. I thought of Thompson standing in the corner of her room wiping back her tears listening to Joni Mitchell. Unlike her, I was able to cry loudly, and I did. But these were more tears of sadness for all the time I felt I had lost, even wasted. It was instantly clear to me that this was my way out. That little promise I’d made to myself watching the film one Christmas had provided me with a much-needed boundary – something clear and true when everything else felt so confused.

That decision to end the relationship was the easiest I’ve ever made in my life, perhaps because I had made it so many years before. For that, I’ll be eternally grateful to Emma … and Joni.