Downplayed: Bob falls in love with Alice, but calmly accepts it when she tells him she already has a boyfriend.
Bob's hoping that Alice will see him letting Charles win and fall for him instead.
There are factors besides Alice's feelings that make Charles more suitable partner. Perhaps Bob has a painful addiction or anger issues. Maybe Charles is rich while Bob is poor, and thus can provide for Alice better. Or maybe Bob's leading a life of crime and doesn't want Alice hurt.
Bob cares more about Alice's happiness than his own.
Bob has a rather low self esteem, and despite Alice being one of the few people he feels confident about talking to, he never truly sees himself as somebody who could make her happy.
Bob is not very easily jealous, and Charles is his best friend. He'd rather see them both happy than ruin what relationship he has with both Charles and Alice.
...Turns out they were just rehearsing a play. Bob really did give up.
At the end of his private rant, Bob sees Alice enjoying the day with Charles, genuinely happy. He realizes he was being immature and selfish and calms down.
Parodied: Both Bob and Charles try to pull this, and they get into a knock-down, drag-out fight as to who gets her.
Zig Zagged: Bob steps back and lets Charles get Alice, but hits on her when they're alone. Then it turns out they were rehearsing a play. But the reason Bob's performance was so heartfelt was because he still loves Alice...