It all seemed straightforward. As I sat down at my laptop one morning last year to write about my toxic friendship, the story was clear in my mind. My university housemates – a group of girls with whom I had lived in my second year – had made my life hell. It was a tale of good vs evil, and they were the baddies.

At the time, I was finishing my book about female friendship – busting myths around every woman needing a BFF, new friends being too tricky to make as an adult and friendship break-ups being a source of shame – yet I still hadn’t grasped the whole truth about so-called ‘toxic friendships’ until I was forced to confront my own. What I discovered left me wondering whether calling someone a toxic friend is too simplistic. Is one person always to blame or did I have to take responsibility too?

The three girls who lived opposite me in our first year student halls were undoubtedly a clique – the sort of perfect girl squad we often see in Hollywood films and on social media. I had struggled to make friends, so when they asked me if I wanted to share a house with them in our second year, I was not only keen but desperately grateful.

Suddenly I was their new BFF. They wanted to lend me clothes and cuddle up to watch films under duvets. I was love bombed – showered with over-the-top affection and attention – and, having been lonely for months, it felt good. So good that when they suggested that we play a devious game to make sure our fifth housemate – another girl from halls – had the box room in our new second year house, I went along with it for fear of rejection.