Everyone's giving you excellent advice.
Like you, I'm the artsy type, with a few radical politics thrown in. I shocked the hell out of a lot of people by Rushing, to the extent that I hid it from a friend for over a semester just 'cause I didn't need her to say that I bought my friends. Whatever. If people are going to be unsupportive, you probably didn't need them in your life anyway...
But, frankly, if he can't handle it and is calling you a sorositute

, it might be time to re-evaulate some things. I understand that Mr. Munchkin isn't a big fan of Greek Life (he thinks it is elitist, and that I could make just as good friends in another activity). The important thing, however, is that he supports MY decision to make it a big part of MY life; he has even befriended some of my sisters. He understands that I am a social person and that I thrive in the environment. After I realized that he understood that, our relationship continued to blossom.
Best of luck with everything!