Bob is gay. Therefore, he doesn't care whether or not Alice forms romantic feelings for him, that's not what he wants from her.
Everyone assumes Bob is only nice to Alice because he has a crush on her. He's just a friendly Nice Guy.
Double Subverted: ... but Alice ends up REALLY forming feelings for Bob, which puts him in a thorny situation.
Parodied: Bob is just an ordinary guy trying, as most guys would, to introduce himself to Alice, but random coincidence keeps him from doing so every single time.
Zig Zagged: Having fallen for her at first sight, Bob falls all over himself trying to impress her. When this blows up in his face, he backs off, mortified. Alice feels sorry for him and encourages him, and they become friends. However, Bob still holds a torch for her, and waffles between clumsy overtures of affection and trying to stay 'just friends', afraid of completely ruining their relationship by pushing too far.
Enforced: "Bob's desperate for affection. There's only one tried and true way to show this."
Lampshaded: "Bob, stop beating around the bush. Tell Alice you love her, she'll either accept or refuse. If she accepts, then keep on being that good, helpful guy. If she refuses, let her go, she's just not what you need."
Exploited: Alice is a Manipulative Bitch who knows how to lead men on to get what she wants and looks especially for Nice Guys so as to seduce them and have them do whatever she asks them to.
Defied: "No, I'm not gonna be the guy that spends two seasons pining over some chick that apparently can't notice me."
"Alice, stop leading Bob on. Can't you see he's just being nice because he loves you?" "But I thought he wanted to be my friend." "Friend? Bob isn't gay, Alice.".
Conversed: "Why is it that so many guys believe being nice to a girl can actually win her over when it's already established that it just never works?"
Deconstructed: Despite being constantly rejected, Bob will just not let Alice go. Eventually, Bob becomes a Stalker with a Crush towards Alice who ends up telling him to stay away from her or she'll call the cops. Bob later realizes that no romantic future had even been possible for them, and that since he could also never have never really accepted being Just Friends either, they should've ended the relationship years ago.
Reconstructed: Bob and Alice sit down and talk about it. Bob confesses his feelings, Alice says he's not what she's looking for and that maybe he's idealizing her a little too much. She says that he should find himself a girl who can actually desire and love him instead of wasting time on her. Bob eventually accepts the situation and both agree to part ways since such a relationship is needlessly hurtful and just can't end well.