Exercise with her and remind her to chew slowly when eating. Eating slowly is easier to get full. You can tell her that wearing clothes (or wedding dresses) will not look good, or tell her the bad consequences of being overweight, but it must be artistic and don't make her think that you don't like her.

Besides, I think it's best not to break up with her to stimulate her to lose weight. I am fat, too. I always tell my boyfriend to help me lose weight. However, if my boyfriend tells me, "I won't want you if you are fatter," he jokes that I won't believe it, but it won't help much. But if he said it seriously, I would be very sad. I'm sure he hates me for being too fat and thinks I'm embarrassing him.

In a word, it's good to help your girlfriend lose weight, but you should be artistic and don't have to be too demanding. It's good to lose weight, but you can't. As long as it doesn't affect your health, let her go, because sometimes girls feel that eating is a very happy thing. Unless you really don't like her, just do your best and don't care too much about the result.