I'm really not happy in my relationship with my girlfriend. She is my only girlfriend I have ever had, and I just cannot break up with her. I've been unhappy for a long time. She starts to cry as soon as I bring it up and she seems all miss innocent again and I just don't have the guts to break up, I hate seeing women cry

I've tried talking time and time again but she say sorry but never changes.
To make it worse my friend(and his gf) let her move into there student house because she had no friends to live with at the time and so they helped her because she was my gf. And I don't want my friends to suffer because of any breakup between us either, and I often go over there to visit my friends
I've felt like this for a good 2year now. Also it's made harder now, because there's a lady who really likes me and wants us to start dating. I really like her too. But i will NOT cheat, i'm not that kind of person, so I explained the situation. I was shocked she didn't run a mile, and she was understanding and has said lets be good friends talk and get to know each other, she said she will respect my wishes and wait before we take things further.