Well, I'm not married, but I used to be really good friends with a guy (who liked me as more than a friend) that absolutely hated the idea that I rushed and hated even more the fact that I pledged and initiated! Fortunately for me, all I had to do was quit talking to him, but since that's not an option here...
I would almost be willing to bet money that your husband is jealous of the relationship you have with your sisters. Maybe he secretly wishes he was Greek and tries to put down your organisation as a means of making himself feel better. Or maybe he thinks that he plays second fiddle to your sisters. Or maybe since there's so many of them and one of him, he feels "outnumbered." Whatever. I can think of a zillion reasons why he doesn't like your sorority, but the thing is, if it's important to you then he should at least try to accept it or not make disparaging remarks about it. Try to talk and reason with him. If that doesn't work, which it might not, just go ahead and do what you want. Wear your shirts, hang out with your sisters, etc. He will eventually see that whining and bitching will not change the way you feel, and ideally he will stop bugging you about it. (That's my mom's advice, by the way--I'm a 21-year-old who doesn't know much, so I went to the higher authority.
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