Hi Kate,
thank you so much for posting here! I'm so overwhelmed and relieved to hear someone going through the same experience I've had. I was terrified while in this experience and have been so afraid of it happening ever since, but most of all, I've felt incredibly guilty and sad about following through with my intrusive thoughts.
I was very attached to a good friend who loved me very much, and I wanted to make things work. He was my first boyfriend, so naturally I was a bit anxious anyway. He lived in another town, and I already started experience intrusive thoughts very early on, only I didn't understand what they were. I felt the compulsion to contact him every single day or it meant I didn't care about him anymore. If I didn't think about him constantly, that made me panic. I was terrified I wouldn't like him anymore by the time he visited me. I was so driven to exhaustion by this obsessing that I hardly even wanted to talk to him, but I had to, or it meant I didn't like him (bad cycle, huh?). I started to forget all the reasons we were such good friends and was just clouded by repetitive thinking patterns, and I was so upset that I was losing all the butterflies and excitement I used to feel.
Eventually he visited for a good week, and we had such a good time. It was so wonderful, and he was so kind. He bought me an expensive dinner, we played like little kids in the street, he met my family, it was amazing. We agreed that we liked each other. But by the time he left, I started having massive panic attacks in the middle of the night. I wrote lists of all the things I liked about him, just to convince myself I still did. I couldn't concentrate on anything. I lost my appetite and wanted to do nothing but sleep all day. I felt miserable.
I convinced myself it'd all be better if I went and saw him, so I did, and we dated for two weeks. But by the end of the second week, I could've jumped in the nearest lake. I was so anxious I was still having panic attacks, and I was convinced I had to break up with him, just because I kept thinking it. I couldn't stop thinking it. I didn't want to, I just had to. Our last three days together we were at his parents house so I had to wait until we could get back so I could leave after breaking up with him, so I obsessed continuously about how to do it, what to say. I savoured every moment being with him, knowing it would be the last. I said goodbye to his belongings. It was so traumatic, I felt so out of control. I had that horrible guilty sense of loyalty every time I thought I looked at another man. I hated myself if I found him unattractive. By the time I returned home to my parents, I was just glad it was over. I crashed for months. I'm much, much better now, but I'm so afraid of it happening again.
Anyway, Kate, I'm just so, so, so happy that someone else has experienced something similar. You feel like you're going crazy. You feel so guilty. And you feel so ashamed because just a minute ago, it seems, you were so, so normal. Everything was running smoothly. And you don't want to blame them, because it feels like it's all your fault and something to be deeply ashamed about. They haven't even done anything.
Keep posting, and I hope someone else contributes some helpful advice :)