It honestly just sounds like you two are co-dependent on each other. You two confined in each other but done have anything more than that. I understand that you have strong feeling for this girl, but is that because she's your only option? If you continue to make yourself available when you want something and she doesn't then it kinda shows that your not valuing your time as much as you should. Because her abusive ex has insecurities and takes them out on her, then in turn her insecurities comes out in stringing you along as devine1966 said. Also it seems like you put to much value in her and not yourself you say "It ruins day to think about her getting back with her ex." You have to give yourself permission at the end of the day to be ok if she gets back with her ex. Because that is her decision and it's not your fault if she ends up back with her ex people will make the decision they want even if everyone sees that its a bad one. You can't base your happiness on someone else and the decisions they make.