he wants to do you
Weird compared to what? Sorry, you are desperate and he knows it. Guys always want to have something on the side, but this is pretty much the same for lots of girls too. For girls I call it 'd*ck in a jar syndrome'. That means, that while girls don't actually sleep with other guys when they have a bf, they usually like to keep a few 'around & interested' just in case. This means flirting and maybe a little more if called for. Actually guys are totally predictable, you may just not want to know this about someone you like. The only time a guy won't act this way (if he has a choice) is when he meets the one or two women in his life time that really make him pay attention. This only happens once or twice, trust me, and there is no mistaking his behavior. If you ever see it, you will know.
He's upwardly mobile?
Maybe he's trying to get his girl jealous for some reason or wants to get in your pants
Unknown knowledge about foreplay and inexperience may the new guys to sex act so weird!
Trying to have his cake and eat it too
Maybe hes just flirting because he likes to flirt.
he just really likes taking to you or is just used to it.
Flirting is fun, even if it is innocent flirting. Especially with someone as hot as you.
He wants someone to fill in for his gf after they fight.