Hello Tom, and welcome to JUB. I'm glad your Google search found us.
Firstly, I agree with SD that you're a good friend to care so much about his feelings and try to figure out what to do to salvage this good friendship. Not a lot of people would care as much as you obviously do, and for that, I applaud you.
Second, I also agree that what you told us could be told to him in an email--or by forwarding to him the link to this thread. I'm rarely an advocate for impersonal communications like texts and email for heady/emotional conversations, but this might be an exception. I think it conveys, very succinctly, your feelings about what's going on.
Third, you'd have no way of knowing this, but a common issue in this forum is gay men developing loving feelings for their best friend. Usually, it's the opposite side of the issue of this thread: The gay man has developed these feelings and wonders how to handle it. In many (most?) cases, it's advised to deal with them on their own and not bring the straight friend into it, because it gets confusing and puts the friendship in peril.
The problem is, you never know what the conscious, or unconscious, motives were in him getting into this friendship in the first place. Did he have neutral feelings for you in the beginning, but then grew to love you because of the loving man (and friend) that you are (he is gay, after all, and being attracted to men would be natural for him to fall in love with one). Or, was he attracted to you from the beginning and that attraction was the fuel he needed to develop the friendship deeper and deeper in his mind?
Only he would know the answer to that--if he's thought about it. The point relevant to you, though, is that, in this process, you have developed feelings for him too, albeit more of a brotherly-love type and totally platonic. But, nevertheless, the feelings are mis-matched.
In the end, he's going to have to deal with his feelings and move them to a plane that isn't driving him crazy, yet able to maintain a fruitful friendship. Sometimes this is possible (gay and straight men have fast and strong friendships all the time without conflicting emotional feelings in the way), but sometimes it isn't.
I hope that he can work this out. There's not much you can do except what you've already done--be kind, accepting, and honest. The rest is up to him.
Just curious--what motivated him to tell you this? Did he just need to get it off his chest? Did he want your help in getting over his feelings for you? It doesn't seem that he held out any hope that you secretly felt the same way, so there must have been some rational reason to tell you all this, and I'm curious if you knew what it was?
Good luck--I hope things work out for you guys.