Why do girls do this? best ans 10 points?

I am not saying I am pretty but do modelling and look ok. wen I am with a uy-any guy-other females will do their best-flicking hair ets, to get his attention often ignoring me. then the guy I am with will leave me, but want me back after a month or so.I know this is a stupid ques and i don't want mean answers, but wat is happening here??