I think it's different for every person and every relationship, PapaBear. There's no formula for how long you should or will grieve or feel guilty or whatever!
I spent the better part of a year feeling bad after one guy dumped me... (I'd like to know how long he felt bad, if at all!) but we'd been together for nearly a year and I really thought we were going to get married. Turns out he wasn't feeling that way AT ALL.