If you play as a female doll, you can flirt with all the guys but not all the girls are available for it (and sorry but most of the girls you can date are lame, lol). Same if you play as a male doll, you can't date most of the guys.
W T F? What's wrong with that?
P.S. If you play as a male doll and date a girl, she won't propose, it's not even an option, she'll say "wanna say something?", so it's up to you.