Dick's a serial monogamist. He is looking for one relationship, which will relegate others to the past, if not invalidate them.
I tend to read Dick a little differently I think, at least in the sense that I don't really see him being capable of retroactively labeling a relationship that had any kind of significance to him completely invalid. Oh, I do think that when he's in a relationship he's completely committed beyond question, hence why the concept of him cheating on Kory with Babs makes so little sense.
But given the fact that he does invest so much in other people, I also think disengaging on that level is more than a little difficult for him. Dick doesn't give up on people easily, and he works far too hard at maintaining positive relationships with everyone, even exes, for me to believe he's really after something to invalidate what came before. Something ultimately healthier and longer-lasting, yes, but erasing the past that got him there to begin with doesn't really strike me as his style.
But in this story, I don't even think it's Dick that's making that judgment; he's pretty clear that while he doesn't regret his past with Kory, at this point in time his devotion and love is focused completely on Babs. It's more the way the story itself is kind of constructed around the idea that Dick/Babs needs the retcon in the first place. He can't just love her now because he loves her now, he has to have always loved her forever and ever, even at the expense of whatever other relationships either one of them might have had before. To me it just doesn't feel very realistic, or true to the things that are actually good about Dick/Babs (in my opinion, of course).