I wish they'd been classes in school to point out the obvious issues in this kind of relationship, e.g.
Firstly, the gay guy somehow thinks that the straight guy is being ambiguous or ambivalent or whatever and that somehow the relationship is going to spark into physical and emotional sexual intimacy at some point.
That just isn't the dynamic of how guys are. Most men know they're sexually interested in someone very quickly, just like the gay guy does, and they don't pass on sexual opportunities, if they come up. Not to say that they have to have sex at the earliest opportunity, but, if the relationship isn't clearly sexual in nature to both participants early on, it's unlikely to become sexual later.
Secondly, even if the guy were gay, it's difficult to move from friends to sexual partners. Because sex is about chemistry, aggression, mystery, etc., it's much less, not more, likely to happen with someone who's already your "brother".
Thirdly, many guys flirt up a storm for the attention and even friendship without any intention of making out. Gay guys do the same thing with girls they sense are attracted to them, not with any malicious intent, but because they like knowing that someone's attracted to them and they don't focus on the other person's internal expectations.
Fourthly, whatever he does, it's rarely about the other person. Most peope accept no, or persistent maybes, as no and know that they don't have to battle to get someone to be attracted to them. Others, from their own family experiences or whatever, are so used to trying to win over unavailable people that trying to do that, and being unhappy, is the norm for them.
Finally, there is hope. Most pepple work out that they're putting themselves into this situation and do it differently. When you're in it, it always seems that the other guy has to be the one. But with hindsight you realize that much of what you thought he was was just your projection and sometimes, seeing how he turned out, you're even grateful that the relationship never went in the direction you were so obsessed with.
Sorry to drone on. Just my opinions, of course.