It's also ok if you and the other girlfriend don't become best buds. It's just fine to be polite and respectful with metamours.
Good on you for being willing to admit jealousy and learnning to cope. Jealousy doesn't seem to go away for many (like myself). It's not a dragon to be slayed once and for all. (And then you get the prince!) Facing one's fears and naming them is a painful but often liberating process.
A small word of warning. You may not be willing to pay any price to be with this man. Maybe poly is not for you or there is some other deal breaker. You seem to be in a good situation but tuck away that some prices should not be paid to maintain a relationship.