He's NOT your boyfriend if he's dating others. Would you really want someone like that in your life? Kiss him goodbye, have a good cry in the privacy of your room, & realise that you'll have plenty of boyfriends & fall in love numerous times before you say yes to the RIGHT man, & you don't need this guy. If he's asking other females out, he's already given you the answer you're looking for here-LEAVE the loser & find someone you can trust-they're out there looking for YOU!
You are worth more than he is giving you credit for! If he wants to date other girls, he is not worth your time. And if he says he won't, I really wouldn't trust him. Follow your head in this case and not your heart.