This is not your child so sacrificing your life for his sake when he’s already failed you several times doesn’t make sense. Not only that, he’s a boyfriend, and you have no legal ties. Does he want to marry you? If so, why? And why, when you have the opportunity to move on and find someone who treats you like you actually matter ALL the time, not just when he needs to get you back in his clutches, do you want to keep hanging in there? Why do you feel so sorry for this person that you feel it’s your duty to sacrifice your own happiness?
Whenever you find yourself in a relationship where you are being abused (and you are), you need to ask yourself what you’re getting out of this. Of course, there are fun times, and I bet he makes some really good apologies, and tells you what you want to hear just about every time he lets you down. What is wrong with you that you think this acceptable?
I know I sound mean, but I’ve been there and I know how self destructive this is. See a therapist for yourself and find a way to get off this merry go round. Life is way to short, and there are some truly nice guys out there who aren’t into a lot of drama and will treat you like you matter.