Ivan & Texastee, and of course, BigWater,
You are both on the money - kind of what I was trying to say. Everyone has one person in their lives that has the "if" factor attached - I don't know why - they are the people who just seem to be able to mess with us. (without any consent from us). They can also get us ticked off at ourselves for LETTING them do that. The first thing is to get on handle on US, (because you're not going to change what they do or how they are, you have to change how you react).
That's where Texastee's "coulda, woulda, shoulda" comes in - work it out in yourself, then - for your girlfriend, for your sanity, for your own well-being, do what Ivan and I said - stop, cut it off, no explanations to her necessary, no conversation, get rid of every single thing that is attached to her. (I think we are assuming that you do not have children with this girl, because that does influence things).
Think of the Al Anon saying - Easy does it and do it. That means chill out about her, because, when you let yourself be angry, you are letting her into your head.
It does sound a little like you two may not have had real closure on your relationship, even so, you need to give yourself closure in your head and your heart. It also sounds like, you are just going to have to do it yourself. (for yourself).
Just try to remember that - what you want is to feel (different from thinking), NO emotions about this person that is toxic to your life, and you need to understand that anger - and even disgust - is an emotion.
Like Ivan said, sometimes we do not learn - or at least, we don't learn right away. We justify things to protect ourselves - its the human thing to do.
It's not that she has gained 80 pounds, or even that she may be a shrew to other people - it's not even about a 350 pound husband. It's about someone coming back into your life who seems to want to screw things up - and might be able to as long as their are emotions there. (not that you are planning an affair or anything like that - its just that those kinds of situations tend to throw us off balance for awhile, and anger is a very strong emotion).
Talk to yourself, get your priorities firmly in your mind - and get rid of anything that pertains to her - from her name on FaceBook, to getting rid of your own anger.
I can tell you, personally, once that happens, it is a blessing. It is a pleasant surprise and a blessing, when the day comes that, when you see this person on the street, or in a store - that you feel...............absolutely nothing. No happy, no anger, no dread, no want for revenge - nothing.
Gotta tell you - that was one of the best days of my life. I still see my ex from time-to-time, now, and I can honestly say, once I crossed that speedbump, it is now like seeing any number of the other people that come to weddings and funerals (the only times I see him), just another person.
B
Rasputin,
Don't you just love stuff like that. My ex did something very similar years ago. Out of the blue. (sigh).