My friend (M19) cries when we have sex and I (M19) don’t want to make him sad

Me and my friend have sex with each other, mostly just to relieve tension. We don’t have a specific arrangement, it’s just something that’s been going on for a couple months. We’re not in a gay relationship, but I do love him a lot and I’ve known him for years. I had a lot of trouble with the whole gay thing at first, and sometimes I still do, but it’s not as bad as before.

The first time we had sex, he initiated it, so I figured he was into guys and that I was just doing it to feel good, but he said he wasn’t gay and I ended up realizing I might be into guys.

The problem is that sometimes when we have sex, I catch him crying afterwards. I asked him about it once cause I was worried I hurt him but he said he was fine and that I didn’t. And whenever we do anything I ask him if he’s alright and make sure I never hurt him, especially when I’m the one fucking him. I hate when he cries and I don’t want to be the reason for it. We were kissing and kind of touching last night and he wouldn’t even look at me afterwards and he apologized like he had done something wrong. I don’t know what to do because end at of the day he’s my best friend and I just want him to be happy.

TL;DR- My friend sometimes cries when we kiss or have sex and I don’t know what to do to make him feel better