The phrase "he wants to snag you"
means that "he" wants to take you away from your boyfriend so that he can date you.
OR if you're single it means that several guys are interested in dating you - each of them want to "snag" you (have you date them).
Basically it means to steel you from a boyfriend or other guys that are interested in dating you.
Once a girl has been "snagged" (dating a guy and no longer available or broke up with her boyfriend to date another guy)
the other guys or the ex boyfriend will say "there are other fish in the sea".
Hope this helps
