Not really, just motivates them to dump the loser
Im in the process of losing the 40 lbs I gained over the course of dating my current bf for a year and a half. I wouldn't say I was fat because a good chunk of it went to my hips and boobs, but you could tell. We're still together.
I guess it really depends on your personal preference. Some people prioritize regular exercise and fitness. I myself, while I wont want an obese man, am fine with a little chunk because I don't like exercising a whole lot except for swimming.
your milage may vary.