I started seeing a bloke I met at a sports club who really chased me. I was a bit 'meh' about him, but was really happy to date and see where it went. The first time we DTD I went back to his house and discovered that his flatmate was a girl he used to date. She was in the living room in her underwear reading something when we came in. He explained that they used to go out and were now "best friends." I thought that's a bit odd, but got on with it.
Over the next few months we saw each other, she was always around and always in her underwear inside the house. She started tagging along to stuff we were doing as a third wheel. I got really bored with her always hanging around (not annoyed, I just found her a bit boring.) One day we all (me, him, her and a couple of other friends) hired a cottage in the middle of nowhere and there was a sudden blackout. I sprung into action, found a torch and lit the fire. Once the fire cast a light on the room again, I turned back and my BF and her were holding hands and kissing!
I started laughing at the absurdity of the situation. I really didn't care that much, I was young and just enjoying the things we were doing together. I told them I thought they'd make a great couple and I was glad they wanted to get back together again and that I'd leave them to it.
I made to leave and he went ABSOLUTELY BALLISTIC. Crying, pulling me back, not letting me out of the door. "How can you do this to me?" he was saying. "I thought we had something special?"
It got to the point where I was was in hysterics laughing and pointing out that he obviously had feelings for his flatmate as they had just been kissing! Both of them refused to acknowledge what had happened, she got on with doing something in the kitchen while he sobbed and tried to block my car from leaving. It was the strangest, strangest evening of my life.
After that he used to call me about five times a day. I only picked up once and told him again that it was over and I'd met someone else. What followed was a huge expletive filled rant telling me I was a fucking bitch for cheating on him, how could I have found someone else after everything we had together. I never got to the bottom of the mystery!
However - I stayed friends with him on Facebook and guess who he eventually married?! Her.