Simple answer: if you're withholding having sex with a guy until he is your bf, and he then asks you to be his gf...well...duh...he's trying to get into your pants. If having sex isnt an issue then he just likes you. A guy lying to get into your pants is a consequence of silly rules.

On asking or not, just do whatever you want. If you'd like her to be your gf, just ask, or tell : ie, I'd like to be exclusive with you. So many guys are afraid of a girl thinking they're needy. Newsflash, if she runs at the thought of you liking her then you 2 were on different pages or she already saw your signs of neediness. A girl can think you giving her a compliment is needy. She can think you trying to fuck her is needy. Stop worrying about what women think, and just do you.