Stockholm syndrome?

I was emotionally abused by the guy I was in love with for 5 years. We weren't together but I thought we were going to be, he flirted with me every time we spoke and told me that if we could be together then he would jump at the chance (my sister didn't want us together), I thought he cared but things just got worse. He wanted to have just sex with me, it would have been my first time so I put it off until I was sure but I never felt sure with him so a few months of me saying I'm not ready, he slept with my sister (took her virginity) and continued to do so, I got upset with him obviously but he had a go at me and said that I'm not allowed to be angry because we're not together. He also came to stay at my house one night when he was drunk and rang me while he was in the bathroom hoping he could come into my room and have sex with me before my sister noticed he was missing, I said no and he slept with her again that night with me a door away. They became fwb after that. He twisted every single argument we had to make it my fault. I was so depressed but I couldn't stop talking to him, there was a point where I was hurting myself because I thought I deserved it for making things go so wrong but I said to myself that I'd rather be in extreme pain than lose him completely.

It's been over half a year since I spoke to him as friend but as he's friends with my sister and we live together, I can't avoid him. I have a boyfriend now who is perfect and I love him so much but I still feel drawn to the first guy, i feel like I need to talk to him. it makes absolutely no sense why I would be other than maybe Stockholm syndrome? Either that or I'm just crazy.

Please help?