I don't think this question makes much sense. Supposedly if you're still in the dating stages, you won't have put on so much weight that it would be quite noticeable. And if you're not attracted to 'thin-deprived' people, you would just not date them in the first place. HOWEVER, if asking the same thing but relating it to a longer lasting relationship, I would say that I would not be bothered by weight gain. At that point you should like your partner for who they are and not be quite so shallow. Though providing some encouragement to lose weight wouldn't be so bad.