The day I found out that Seth was cheating on me was also the day I told him I loved him.

We had woken up at his place, all limbs entwined and sheets tangled up, and I was feeling woozy with happiness. He had a lecture to go to, but I remember that he missed it. He told me that I was teaching him more about love than anything Shakespeare had written could possibly hope to, and I thought that was so romantic.

I had never told anyone that I loved them before except for my folks – and it wasn’t even something that I said to them all that often. So, when I blurted out those three words to Seth that morning, it was a big deal.

A really big deal.

The rest of that day, I floated around London. I felt invincible, you know? Like I had worked out the entire meaning of life, and wanted everyone else to feel as good as I did. Hell, I probably even sang, I was that happy.

After I’d finished work that evening, I got on the bus and went straight to Camden Town. I had arranged to meet Seth in the World’s End pub – an ironic choice of venue, as it turned out – but bumped into Lavender on the way in. I knew something was up right away. She seemed so twitchy, like she had a whole nest of ants in her smalls, and she couldn’t look me in the eye. We got ourselves a couple of ciders and went to the table where Seth and his other mates were, and right away Lavender starts goading him, making all these snide little remarks under her breath, saying stuff about all the lies he told, and that he owed her because of the trouble he’d got her into with her parents.

It was so weird, because the two of them usually got on great. I mean, she often teased him and told him off, but it was always in good humour. I became aware very quickly that she was right raging angry with Seth for some reason. And I wasn’t the only one who noticed – everyone was looking at each other as if to say, ‘What the bloody hell is her problem?’, and I’ll be honest, I didn’t really know how to handle it. I just knew that something was wrong, really wrong – I could feel it in my gut.

After this had been going on a while, Lavender got up and went to the toilet, so I followed her. I thought I’d try to cheer her up, you know? Snap her out of it. I was still trying my best to hang on to the happy mood I’d been in all day, but as soon as I asked her what was up, Lavender started going in on me, saying how stupid I was, and how Seth was making a laughing stock out of me.

Well, that really wound me up, and I’d had a few drinks by this point, so I argued back for once. I told her that Seth would never do that to me because he loved me, and that he’d told me as much that very morning. When I said that, her face seemed to crumple in on itself. I had uncovered – and shredded – her last straw. From the look of her, I thought she was going to start crying, but instead she just laughed, and it was this really cruel and hard laugh.

I went cold all over. I’m cold all over now just remembering it. Her reaction had scared me, and so when she tried to keep on talking, I ran right out of there. I went back to Seth and told him that we had to go, that I needed to leave. I just wanted to get him away from Lavender before she said anything else, but he wouldn’t listen to me. He was drunk, and showing off as he always did when he’d had a few too many jars. Talking rubbish while all his so-called friends rolled their bloody eyes at him.

Lavender came back from the bathroom with this dangerous air about her. She’d not long ago dyed her hair bright blue and that night she had spiked it up like Jack Frost. She was all sharp edges and icy colours that night, and she fizzed with self-righteous anger. I could feel it coming off her. Seth apparently couldn’t, or didn’t want to, because he just laughed at her, all scornful and dismissive. I will never forget the look on her face when she turned to me and calmly told me to ask Seth what had happened in Brighton.

I was confused, because as far as I knew, he had gone off to Brighton on his own when I couldn’t go with him. It was after that weekend that he’d started being really sweet to me. I told Lavender to shut up then. I was fed up with her for ruining my day, and I was too frightened to have any desire to hear Seth’s answer. In the end, though, he didn’t say a thing. Lavender sighed, and said that she had to tell me – and she did. She told everyone at that table how Seth had invited her to Brighton at the last minute, and how they had spent pretty much the entire weekend in bed together.

I almost hurled. The blood just drained right out of me, and I tried not to cry, but it was as if I had been possessed. I was wailing and screaming and shouting at both of them. Seth tried to grab my arms, but I found some superhuman strength inside me and managed to pull away from him. All I could think was that I had to get away from both of them, from her need to hurt me so inexplicably, and his pathetic lies as he tried to persuade me that she was playing a trick on me – that the whole thing was some sort of sick bloody joke.

I ran out of the pub without my jacket, and the bus was right there at my stop, so I got on, and I saw Seth out of the back window, chasing up the street behind me. I loved the guy so much that I wanted nothing more than to get off, but I knew that Lavender was telling the truth.

The signs had been there all along, but I had allowed myself to become blind to them. Even when I knew Seth was manipulating me in order to get his own way, I excused his behaviour. I thought that’s what love must be, and that his need to control me was fuelled by genuine affection, but there was always a small voice telling me that things weren’t quite right – that I should want to have sex with him rather than feel as if I owed it to him. My worst fears had come true, and having all my horrible insecurities confirmed in such a cruel way had upset me, of course, but it had also made me angry. I was fuming.

I went straight back to my home away from home, where I knew I would be safe and looked after. The professor, who I’m sure by now you have worked out is David, was shocked when he saw the state of me, and then he was furious. I didn’t know he had it in him to be so cross, but it made me feel better, seeing him so affronted. It made me feel as if I was worth something after all, even if Seth clearly didn’t think so.

Once I had stopped my crying and we were talking it all through, I started to feel even angrier – this time on David’s behalf. I was pissed off with his wife for the first time. Because how dare she walk out on him? How could she blame him for something that was nobody’s fault? I told him what I thought, too. I said that she was stupid – even more stupid than I had been to put my trust in Seth – and he did the oddest thing. He started laughing, then he picked me right up and swung me around, said I was the first person to ever take his side, and that me being cross meant that he could be cross, too. He needed to shout – we both needed to – and that’s what we did. We yelled and we swore and I think we even smashed a few glasses. It was cathartic, and even though it was the worst day of my life, it somehow became one of the very best.