I don't think it's an all or nothing situation. It's not either you are nice or you are jerk. It's looking at how your "nice" effects the relationship. If your "nice" means you never have conflict, are agreeable to everything, never disagree on any subject, or you are continually doing things just because she wants to then those are things to look at. Being nice is not nice if it is covering up who you really are. Anyway, I have no idea whether any of that is you or not BA, just sayin' don't disregard being too nice as a legitimate reason to end a relationship. Being too nice can also be known as "the disease to please" and it's a relationship killer! Hey, your lady was a nurse, right? So was mine.
