Weight loss for him...

My boyfriend and I have been together for a few years now. A while back I had a miscarriage and long story short we broke up for some time. In that time he kind of "let himself go" and gained quite a bit of weight. We got back together but he still seems to care less and less about the weight gain and his overall health. It's almost like he's proud of it? How do I bring up his weight and health to him without sounding completely awful? It's gotten to the point where some positions in sex are hard to achieve because of the gut and his and my sex drive are lower... Help?