What do I do if I am becoming unattracted to my fiance'?

If this is really a health issue, he needs to start eating better and exercising. He can't complain about his weight and then refuse to change his unhealthy habits - it doesn't work that way. I have a friend who does the same thing - goes up and down in her weight drastically because she doesn't want to make that life change, and it's taking a toll on her health.