Is it Shallow or Legit Expectations????

You're in a relationship. You've always been attractive to your partner from day 1. But as time progresses they start to put on weight.5 lbs, 10lbs.....30lbs. Is it foul if you no longer will attracted to this person. And if so how do you handle it? Would you stay? Go? I'm leaving the type of relationship and other details open to interpretation to get a wide array of thoughts/views.