Weight gain in a relationship!

A relationship with initially a great fitness plan and health, and great physiques. Sadly things happen in life and many turn to food as  process for comfort and pleasure. Easily with one gaining weight rapidly a relationship can turn sour. Ie love, hate, cheating, abusive, separation etc. Why so much pressure?  and in  many cases negativity surfaces, jusy to be and look a certain way to love and be accepted?