It seems to you that your boyfriend is overweight? And you have no idea what to do? Well, it depends on him but it even may hurt him if you share your worries directly. If he doesn’t takes the hints then you have to say him he should lose the weight. It doesn’t work as well? You have tried already several times? Then you have to be persistent because it concerns not only his physical appearance but mainly health issues. But if you are overweight yourself and blame your boyfriend then it wouldn’t work definitely. I mean you should start first. Otherwise you have no right to require something from him. I think it is obvious. Explain him that it would improve not only his physical appearance but his mood as well.