Pretty much classic friend-zone stuff.
Your buddy might think he's miffed because she didn't treat him honestly, but he put her in a mildly awkward situation that she didn't handle particularly well. The reality is, he's probably hurt that she didn't return the affection immediately. Either way, this is something he can and should forgive from another person he likes and wants to be friends with. It's a minor mishandling that wouldn't even need to be addressed if feelings weren't involved.
I'd forgive the girl, not change my habits with her if I really liked her, and I'd keep offering opportunities to hang out that could lead to a deepening of the relationship. I wouldn't mention my feelings again, because he's made it clear that he's interested. If there's a right time, I'd go for it, and respect her feelings if I got rebuffed. If the issue comes up again, make it clear that I both like her as a friend and am interested in dating her if the relationship evolves, I'm going to for it. If that's uncomfortable and she'd rather not hang out socially at all as a result, I'd be bummed, but I'd understand.
At the same time, I'd keep my options wide open. If there's another woman who's at all cool in the same environment, I'd make overtures there, too. From my experience, people want what they can't get, and the threat of losing affection to another woman is a powerful aphrodisiac. To go this route, though, there's an important balancing act in being fair to both women.
Either way, the guy needs to nut-up, stop letting his feeling get hurt, demonstrate to the girls that he's desirable on his own merits, and go out to find someone who can make him happy.