Yeah, amazing game though it is, Dominion is just a game. Winning Dominion is way less important than having a happy fiancee.
Having been married a few years now I've learnt that there are certain games and play strategies I shouldn't play with my wife. Any game with multiplayer tabletalk is a bad idea, as she takes it badly if I manipulate a game to engineer an alliance against her while she is in the lead. Likewise, she knows that I like to play my games seriously, so she doesn't (any more) do things like "I'll trade sheep for stone with your brother because he hasn't won any games for a while". As far as I'm concerned, you play for your own victory in the current game, and to play kingmaker at cost of your own chances of winning is not good gamesmanship.
On the other hand, neither she nor I have problems with cut-throat attacks and game effects which potentially sap opponent fun (like IGG or Torturer).
So yeah, compromise is part of marriage. Compromises don't have to be even or fair either. Your fiancee is allowed to be a bad loser or to feel that she can play strategies that you can't. Is it fair, and is it something you'd put up with with a friend doing? Probably not, but serious relationships always have little sticking points, and its the whole thing you look at, not the little details.
Games are just games, and the goal is to have fun. Is a clash in gaming styles something which makes it worth an otherwise happy couple fighting about? Probably not!
Also, of course, I pick my gaming buddies because they game in the way I do, and thus we don't have to clash over different gaming philosophies. I picked my wife as my wife because I fell in love with her, and gaming didn't have much to do with that. I play games with her occasionally, but in a different way that I game with my gaming buddies.