First of all, I can relate.
The thing is that worrying constantly isn't going to change anything. Either he is cheating or he isn't. You'll just drive yourself insane playing the "what if" game.
If he's lied and cheated before, than your fears are valid. but thise kind of thing makes non's run in the oppisit direction from us. So my advice is pretend like it's not on your mind. Set a trap to catch him if you need that piece of mind. If the trap yealds nothing then you either need to forgive/trust, or you need to move on because it's gonna get ugly other wise.
Second of all, I know it feels like you can't be alone, but in actuality you can. It's called "tolerating the moment'", it's a DBT skill. It's easier said than done, but with repeted practice it can be pretty helpful. I know full well all about the painful in the chest please don't leave me alone feeling, it's overcomable.
Best of luck and I'm here if you need a friend.