Questions: Break Up & Divorce

When a girlfriend and I were together, she allowed me take some rather beautiful and provocative nude photos of her, including some where she was giving me head. Now that we're breaking up (or at least seeing less of each other), she wants all the digital files back. I don't want to be a jerk about it (we're still great friends), but I also wouldn't mind keeping copies as mementos (I'm a connoisseur of the female form, as well as a sentimental fool :)

I have absolutely no intention of sharing or distributing her photos as they are very personal to me (as well as to her) and a lawyer friend of mine assured me that I have no legal obligation to return them so long as I have no intention of distributing them or making them public. He points out that the photos were taken during private moments in her life, which also happen to be part of MY LIFE as well. The courts call it "joint custody" -- so the most I would have to do is give her COPIES of whatever photos she wanted.

That said, does anyone think that I should still give her back all her photos and files? Should I really allow her wishes to supersede mine, even though we legally have equal rights to these lovely mementos?