How to apologise to a girl who was my best friend and room mate?

I was best friends with my room mate at uni so we decided to live together in our second year. Her boyfriend moved in with us the day after we moved in and stayed for 2 weeks which I got told would be a few days so I was upset...then he had friends over and after having quite a bit to drink, they started saying inappropriate things to me and no one stuck up for me so I walked out and didn't talk to them both for a few days. This ended up causing a huge rift between us and when her boyfriend got his own place she practically moved in with him and I didn't see her for about 5 months and ended up living on my own really far away from my other friends and my boyfriend. I decided to move out and after I did, someone told her things I'd said about her and how her boyfriend manipulates her when I was very upset and she seemed really hurt by it and that made things awful between us and we haven't spoken since the last time we argued about that when I was moving out. I feel awful and I want to write to her and apologise for having hurt her but I'm afraid that if I do it will just sound like a huge joke to her and her boyfriend and I won't hear from her again. Please help, I really want to patch things up with her.