Re: I need to get some stuff off my chest and maybe some advice...
When one of those telemarketers calls to offer you a magazine subscription, do you:
1. Buy everything they offer, because you want to be nice
2. You politely thank them and ask them not to call you, and then end the conversation asap
3. just hang up without saying anything. You don't even say "I am not interested".
I bet, you are somewhere between 1 and 2 :-)
And you should be in the 3. category.
People like you are very rare, especially men. Others would've cheated on her, wouldn't even blink about the abortion-pill thing, and would never humbly ask for advice here.
What's obvious to us is probably not obvious to you: you don't owe that girl anything any more. It was different when you were together, living together, and when some sort of commitment was implied. But that's in the past. There are no bridges, so there is nothing left to burn.
By now you've probably figured out that you need to step away from people who are hurtful and who don't respect you and that you don't have to look back once you do that. That's the least of your problem.
The real issue is this: in being understanding, responsible, sympathetic and loving, you have forgotten that every one of those qualities needs it's polarity. If you are understanding on one hand, you also have to be careful on the other. You have to be cautious to make sure that your good intentions are not taken for granted or used against you. That part seems to be missing from your life.
The first time she attacked you, when she hit you and called you all kinds of names, that was the moment when she showed disrespect. If she apologized, but later did it again, you knew that apologies meant nothing to her - she just used them to have you as her doormat.
You have a right to be with someone who is equally understanding and loving and caring, and you don't owe abusive people any explanations. Burning bridges is a term that refers to people who you may not see anymore, but who you had no major problems with. But when someone doesn't mean well, you are way beyond the problem of burning bridges. And since they don't care, you shouldn't either.
The lesson to learn here is to take care of yourself first and foremost and stay well away from toxic people. Vast majority of people in this world feed off of people like you - those who are willing to be put down, called "stupid" and who are willing to feel guilty for something that is not their fault (like that abortion pill). Often parents are like that towards their own children - they turn their abusive attitude towards their own child and the child becomes sensitive towards others but desensitised to his own pain. You may love your mom, but I would be willing to bet that deep down she was not much different from that girl you were with, and was in some way abusive towards you (emotionally). Then you learned from her to accept it in others as "normal". But you don't have to. Learn to recognise people who like to abuse others through put-downs, agression, name calling etc, and learn to walk away from them. You don't owe them anything. Not even a "bye".
You don't have to call her, she wants you to call her - whatever the reason. Just don't call her, and hang up if she calls. If she is in your apartment, then kick her out, pronto, no emotions, just tell her to leave immediately. If she makes troubles, call police and tell them you are not in a relationship, she came over and forced her way in. In dealing with people who are disrespectful and abusive, you have to protect your interests agressively, and free of emotions.