My gf is morbidly obese what should I do?

Trade her in? Girls aren't objects you can just trade in. And girls are not there to 'service you' Have you talked to her about it? Maybe you can suggest going to the gym together. Don't dump her just because of her weight. If you still have feelings or her then you should try to work something out. And if you do decide to dump her I'm sure she can find someone better who actually cares for her.