Hang in there
My wife has been overweight most of our 28 years together. I love her very much. She has given me 3 beautiful sons who have grown up and left home. Her being overweight has never and will never make me love her any less. Just because you are overweight doesn't mean you are not a beautiful person! There is more to life than looks, trust me. I agree with maleficent. You just need to accept yourself, be happy and then you will gain confidence and later, the motivation will come. So just be happy you're alive and have a fiance who loves you! Everything else will fall in place!
Best of luck to you and you.
-Bill