marriage (or civil union) is an official thing, and at least in theory, has aspects of being publicly known and permanency, while gf/bf or any other variations do not. It is not TMI for that reason (as in you cannot really cannot be discreet about being married, it is there :P) It might be my language confusion but I see the word "partner" as a gender neutral way to indicate a husband or wife (as one of its meanings) and in that context that too is okay.

Hope this makes sense?