I'm a 40-something M2F transsexual woman (though my gender status isn't that important). I recently met a great guy I'll call John and I've developed feelings for him. I'd jump his bones in two seconds except for one thing; he's HIV-positive.
It would be hard to come up with a decision more individual and personal than this one. Plus, this isn't a situation where I can pooh-pooh your concerns. Of course you have concerns. I have them for you.
Although having some sort of sex with an HIV-positive person is hardly risk-free, it is undertaken nightly by thousands of people who never sero-convert. There are condoms, and condoms are quite good at what they do. And there are all the noninsertive things one can do that are more or less incapable of introducing any virus. It may not be what you want, but it's doable and, under the right circumstances, you can build a sex life based on what you've got rather than what's missing.
If your big fear is not contracting the virus yourself, but loving somebody who already has it, there is no cute trick with latex or frottage that is going to fix that. Most any article you pull up on the subject is going to contain the statement, "HIV is no longer a death sentence." Which is true as far as it goes, but it's not like it's no longer a problem. Either one of you could be hit by that bus that always crops up when people are discussing the capriciousness of fate. But he could also stop responding to his meds, or develop debilitating side effects, or follow some other course we're not too up on yet because it occurs 40 years after starting therapy and nobody's done that yet. We don't know. And we, being human, like to.
But this sounds like something you can't just walk away from — you have, as you say, "developed feelings." But neither is it something you can just walk into. If you're going to make a go of it, the two of you are going to have to get a therapist with expertise in exactly these issues and work through some stuff. You're going to admit your concerns. To him. And he's going to have to admit whatever it is he feels about the prospect of undertaking a long-term threesome: you, him, and HIV.
On other hand, you two are not officially an item yet. You do not have to do this. He probably wouldn't think less of you if you decided you couldn't hack it. Well, OK, actually, he might, but you can't make a huge decision like this one on the basis of conflict-avoidance.
On the other, other hand, it's possible your decision will get made for you when you spend more time together and find that he's hopelessly argumentative about baseball trivia or in some other way not nearly as dreamy as you thought. And then you can ditch him with a clear conscience.