I'll echo what the others have said above, ultimately you need to make a choice.
It's understandable that you have some concerns about Adam's positive status. It's not always rational even though he's undetectable and on medication. However, those are your hang ups. You can't then say your sex life isn't what you want it to be when you're the one who is ultimately putting blocks in the way. Like I say, I understand your hesitation to a degree, but if you care about Adam the way you say you do, then surely it's worth putting in the effort to work through those issues? Don't use them to excuse your behaviour.
I get the impression you don't want to make the hard choices, but unfortunately, that's life. You can't have it all, you even said so yourself. One way or another, this is probably going to suck for you. I'm sorry if that sounds harsh, but I think it's the reality of the situation you put yourself in. You need to step up and make a choice. Yes, it will be hard and there may well be consequences to the choices you've made so far, but the sooner you accept that and take the step, the sooner you can move past this situation. Because at the moment all you're doing is delaying the inevitable and hurting people in the process.
I think from your post you know what you need to do. My advice is to be brave and get on with it. These things have a way of coming out eventually, and by then that choice may not be yours to make. You could potentially end up in a worse situation than you are now.Try not to let it get to that point.