How do I gently bring up the lack of sex with my (male) partner?

I have been seeing someone for the past few years. We are NOT in a committed relationship so I have had casual encounters with men, but me and him have a very strong romantic/personal connection. Just to give you an idea, we spend all birthdays and valentines and other major events together. We all know each others friends. When we started out, we had wonderful sex all the time, but it has dropped off completly. There are several reasons why: he has started a new VERY demanding job, he changed SSRIs, and he has gained a lot of weight ( I think all of these issues are connected). For the past year, we basically never have sex at all. He brought up that the new SSRI makes it hard to become hard and I think he feels insecure about it. When we do have sex, he very rarely takes his shirt off which makes me annoyed because I LIKE his body and want him to not be shy about it! I know he isn’t seeing anyone else and I know he cares about me, but my gentle comments aren’t working (I will say “I miss when we had sex” or “I am so horny for you”.) I don’t want to push or embarrass him but I need to have sex but I do not want to give up on him completely. Men, how would you want to be approached? Any insight? Women, have you dealt with something similar? Any advice very much appreciated.