Personality goes a looooooooooooooooooooooooooooooooooooong way, fat or skinny. I know MANY fat chicks in long-term relationships. I don't know you, but one thing I have learned in life, if you can't keep a boy/girl friend...then, it's you and not them. I've met many people from all sorts of life, even some people that the masses would consider "ugly as fuck," and even those people have great relationships.
If you put yourself in a box and say you can't keep girl/boy friend, then 9 times out of 10, the problem is YOU and YOUR PERSONALITY. Learn to compromise and quit trying to please at the same time, and you might realize that it's all about personality and not how much your thighs rub together when you walk.