I think the most important thing you can do is follow NOP's advice. Stay calm. This is going to test your patience beyond belief... but there is a side to him that has GOT to continually test you in order for you to reassure him.
Don't try to understand it. You cannot apply logic to an illogical situation. Stay calm. Stay pleasant. Keep doing what you are doing, keep going to counseling... if you need to vent, do it here.
No one here can fathom his instance on hanging on to these memories... but... that is irrelevant, like NOP said. He is in an endless loop, and I'm SURE he wants out of it as much as YOU want him out of it.
Plus... like I also said before, it is a convenient deflection for his own behaviors.
You have to be SMART about this girlfriend. Don't REACT. Respond. Fix this. And when you do, which you will... tee hee. He's got his own stepping up to the plate to do.
