I hear you regarding old correspondence. Heck, I have emails from two weeks prior to the bomb which assure me W "will love me for years".
Recently my sister did an audit/"his-hers sorting" of old memorabilia and that put me through the wringer seeing old love letters from when we were 16. But you know, mixed in were a lot of great letters from other friends and it actually helped me remember how many people care about me--and one of them provided a clue to find an old friend I'd been searching for for over a decade, and it was great to get in touch with her finally (innocently, people!)
While it hurts tremendously, it can be sometimes good to remember that things used to be fantastic. It helps me believe that my M is still worth fighting for, because right now it just seems an endless supply of pain.