My bf is getting gaining weight

How do I tell my boyfriend he’s getting extremely overweight to the point we can’t even do activities together. We couldn’t go zip lining because he’s to big so we went water rafting which is fine to me. I knew he was kinda sad about it so a few months later I Joined a gym and I go just to go so he can see me go and I actually like it so I go on a reg and invite and he never wants to come. I tried jokingly tell him he’s gaining a lot so I won’t hurt his feelings but he’s not getting it. He’s 326 and he is 6’3. I meet him when he was 256.

Well here’s an edit since people think idc about his health lol. We been together for a year and we tried the healthy eating, walking and all that. We sat down and talked about his health because his father had chronic health issues. One point he use to work out a lot and be healthier way before he meet me. So when I’m at the gym he will sometimes be on the phone with and tell me what to do.

I know way back I asked him if he was depressed or stressed he keeps saying no.

I mentioned the activities because that’s what triggered him to tell me he wants to lose weight because he was embarrassed by it but he doesn’t take action towards it.