No one likes to be used. Learn from a dating coach's advice how to stop getting used by your partner. Explore your options through advice to a real reader's question.
The best predictor of future behavior is past behavior. Now that your girlfriend lives her life being unfaithful, her behavior is not going to change no matter how much you love her. She has the personality that can tell a man what he wants to hear, then uses, and abuses him, taking advantage of his love, finances, babysitting, etc. to suit her needs. You are the victim of a woman who preys on kindhearted souls. To put it bluntly, you're being taken advantage of and allowing this to happen! You're being a doormat.
You can decide if you want to continue being taken advantage of and having your heart broken or if you are ready to do something about it. First, accept that she is not going to change, no matter how much you want her to. This means you have two choices. You can stay in the relationship as it is or you can give her one chance to change her ways. To do this, you're going to need to grow a backbone and have a talk with her. You would have to be willing to tell your girlfriend, "I will not stay in a relationship with a woman who is unfaithful, living with another man, and doesn't prioritize her own children. If you don't change your behavior, then the relationship will end." Give her a time limit or date by which she has to show (not just say) she has done what you asked.
Once you have given her a choice to change and keep you or not change and lose you, you must follow through. If you don't, she will know that you are weak and she will continue to say what you want to hear without ever changing her ways.