Hi,
After reading your question I concluded that:
1. Both of you are immature. You are 19. (No offence)
2. That he does not truly love you, he plays with both of your emotions( the other girl's too)
3. He is using both of you for sex , free sex with no committment in mind. As long as you allow him to disrespect you, then he will keep doing this. You have to prove to yourself that you respect yourself.
4. That you at 19, are not using your energy into trying to improve your life. You need to think of finishing college and landing a high paying job, so you will be financially stable when you are actually ready to marry when you are 27 years old. This kind of relationships are very normal, love relationships. Everyone had experienced this before. But you should not let this be in your way in thinking for your bright future by shifting your efforts and time to a more productive undertaking as in going to college. You will gain knowledge, insight and experience and you will look back later on and conclude that what you are doing now is a waste of your time with this man.
So in essence, I am advising you to:
Leave this confusing relationship and go to college, be who you want to be, someone who will command respect and a positive part of society
that fosters LIBERALISM.
Take care and do the right thing.