A2A. Look, being a good guy isn’t about hiding your feelings from her until she deigns to sleep with you. If she’s got two functioning brain cells she’s going to have already put together the fact that boys like sex and most of the boys talking to her are going to want to have sex with her.
If a girl likes you but isn’t interested in sleeping with you, then you’re a nice guy. Doesn’t make the guy she does sleep with not nice, or nice. There are all kinds of reasons why girls sleep with boys. It’s not a ‘nice race’.
You need to not attach your feelings of self-worth to whether a particular girl will sleep with you or not.