I can understand what you're going through. I had a roommate in college that hated all greeks with a passion. I rushed informal, so I only had to go to rush for two nights. Anyhow, I would sneak out of the apartment, and if they happened to be there, I would just tell them I had something to do, but never told them what. Well, it just so happened that the night that my bid was delivered, she was up late watching TV with me (which she hardly ever did during the week) and that is how she found out I was going to pledge. She was really awkward around me for a while. Hindsight being 20/20, I now realize that she thought I was not going to ever have enough time for her anymore and that I would soon be spending ALL my time with my sorority. Long story short, she got over it and realized that there was room in my life for my sorority and her and we are still the best of friends and she'll be one of my bridesmaids in September.
I also got a lot of ribbing from my boyfriend's (now fiance) friends. I just took that in stride because that is the way they are and they soon got over it and one of them commented later to my b/f that I was a lot less reserved and so much happier and entertaining. I used to be very shy and quiet. The sorority had given me more confidence and loosened me up a little.
My friends had all of the misconceptions that you stated, but I'd like to think that they have reevaluated their view of greeks because of me. Hopefully you can do the same for your friends.
If I had it to do over, I would definitely do it again, but probably be more open about it with everyone
Good luck!
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"Would you not like to be sitting on top of the world with your legs hanging free?" -- Dave Matthews