First off, Jaeger, you make me laugh with the Divine Brown comparison. LMAO! Call it as it is.

I call that whoring too, and at least get paid for it.
But on a more serious note: No offence, but either you're drama or you surround yourself with drama. If it's the latter, that still makes you a drama King. You also have the "why me; sorry me" attitude. Stop wallowing in pity. Either you suck it up and stay in the relationship or you wear the attitude you need and leave the relationship.
Let me say that I agree with other members who have pointed out that people tend to blame their so-called partners' accomplices. I too think the blame should go to the right person: Your significant other. You say she's to blame, yet you keep making excuses for her conduct. I want to pop the heads of some ladies that fight the the mistresses rather than their significant others. The men have it so easy. It is your significant other that's supposed to be committed to you.
Well, that of course is an assumption. If your significant other isn't your spouse, then you have no business whining if you had no oral or written contract that the relationship was exclusive. I'm sorry, but it's hard for me to sympathise if you were presumptuous and thought she was committed to you. I don't remember her making a vow to you. You aren't married to her, so stop crying "why me; sorry me" and leave the relationship! If you choose to stay in it, too bad. I won't even just say this if she does it again. I would actually laugh at you again. You make excuses for her and say it isn't disrespect. Maybe it isn't after all since she has no obligation to you. From the sound of it, this isn't the first time she's done this. She's just giving you what you seem to want: Drama. If you're surrounding yourself with drama and sources of drama, then it's what makes your life and brings happiness to you. So maybe you're benefitting from her so-called selfishness too. MichaelD was right, but it's applicable to both men and women. Besides, I don't think it's a good idea to give credit to a bitter old man. LMAO! Hahaha! I like to tease MichaelD! Sorry.

He actually seems happy now and well relaxed. Maybe his last gf put just too much stress on him and he had to blame it on the mother of his kid.

Anyway, Jaeger, I would normally sympathise, but you sound too much like Mr. Saviour, Superman type of guy (translates to drama King). I don't like drama Kings and Queens, since they seem to do everything for credit or attention. Hope you can resolve this matter and feel better soon.
P.S.: Is this lady your first love? It sounds like it. If so, it would explain your whole "it's hard to get over her" cry/attitude. Yes, it would be hard to get over her in that case. But it seems you don't have any kids, so take advantage and leave now.