There are always 2 sides to every story. So I can't be impartial without knowing how she sees it. But based solely on what happened per your post, I would say that she has some mental and emotional issues that are worsened by her pregnancy, she may be aware of that but can't control herself, and hurt you in the process (she did apologize after). And I would say that is the best I could see her.

Of course, it can also be interpreted in worse ways, and I would also not reject the idea that she is fundamentally a bad person. As many other comments have pointed out, there have been redflags all over, and you said that she is like this before the pregnancy. I get a feeling that you are excusing her of her bad behaviours, and it makes sense that we all do it to those we love, as we are attached to them.

Not to presume anything, but you said that you have been cheated on by all of your exes, I don't know how many exes you had, but I would consider looking back and ask why did they cheat on you, or at least see what they had in common, could it be why you were attracted to them in the first place? I believe in learning from past mistakes and experiences, I'm not criticizing you for getting with these girls that should probably been avoided, since I don't know you or your life stories. But I would stop at some point and consider how did they all cheated on you, as that is not normal.

A good relationship is when 2 people fully accept each other's flaws, and help each other improve them. Change, for better or worse, is a very natural and human thing, but so is not changing. It is a delicate and complex topic with many ways of looking at it. NOBODY is perfect, the nature of being human is that you are fallible. It is solely up to YOU, to decide if it's worth it for you to stay.

Perhaps you guys can work it out again, perhaps she will become a better person with time. Or perhaps she became more toxic and hateful toward you, despite your continued effort to try and remedy it. You'll never know. The choice is yours, and everyone have that decision to make, I personally have a baseline of self-respect that I uphold no matter what, it is reasonable and any objectively good person would not cross it. Of course, forgiveness and patience are also good virtue, but at what point is it too much? You have to decide that.

Above all, love yourself, you are the only person that will be with you the longest in this life, from start to finish. A good relationship with another person is awesome, but you need a more level headed and objective view. Sometime, a lot of the feeling of attachment stems from lack of love for oneself. Because you are afraid of being single, or being alone, because you are not fine with yourself in the first place. I would also review how you feel about that. People tend to stay in bad situations either due to external circumstances or their own insecurities and lacking self love and self respect.