If I'm on a B1 B2 visa which is expired but my boyfriend has a green card, can I get married right now or do I need to wait him to get a citizenship?

There is no need to wait. The petition by a green card holder, however, has lower priority than a petition by a US citizen. A green card holder's petition will have to stand in line for a visa to be available, whereas an approved petition sponsored by a citizen will make a visa immediately available for you.