Paulie, you're too young to stay with a primary partner who has such jealousy issues. From my own experiences of being 20, at that age you don't really know yourself well enough to be stuck with someone who won't let you explore and live your life the way you want.
If you were, say, 40 and had kids and a long history with your primary partner--then yes, it might be worth the sacrifice to work hard and make compromises to stay with your mono partner. But why do that when you are only 20?
Your case is a good example of why rules like "you can only date girls, not guys" make no sense. Some people are transgender, and their genitalia shouldn't be an issue!
I suppose you could offer your partner the chance to do some hard work getting past his jealousy (and penis-related insecurities), but I dislike the fact that he was so callous about people you dated. Why does he think it's okay to make you dump someone? Doesn't he care that it would hurt both them and you?
There are so many AWESOME poly-minded guys (and people of all genders) out there. Why stay with someone who sounds so...lame?
Single, straight, female, solo, non-monogamous.