It's amazing the kind of affect a woman with options has on a man. If you believe that he isn't the only fish in the sea, a real man will become his best self in order to make himself the BEST fish in the sea (and therefore worthy of you). This shouldn't be mistaken for treating a man poorly, and it doesn't mean it's ok to go out with other men with the sole purpose of making a man jealous. This is manipulative, and it will backfire every time. No, you just need to let him know, through the way you treat yourself (among other things), that if he isn't the kind of man you deserve you won't be pining away for him after you break up.