Dating frat boys
All the girls I casually dated when I was in a fraternity I met through friends.
Some of them happened to be in sororities but that was just a coincidence.
She was hit on by a lot of fraternity guys but it never bothered me because we had full trust of each other and she never gave any attention to them. It generally rejects the "serial monogamy" loyal girlfriend / loyal boyfriend norm that young people today impose on themselves as early as middle school.
I remember I would go to their various sorority events and every other dude there would be a fraternity person, and I would immediately be an outsider. I got invited to events that I normally wouldn't be allowed to go to.
What was worse was when her sorority would do common functions with a fraternity, and she would want to go with her girlfriends, but I wouldn't be allowed to go, so she would either have had to go with a guy from the fraternity, or not go. TL; DR - Just fuck her casually, but don't get involved. I trusted her enough so it never bothered me when she went to a party or something without me.
There were plenty of times she'd go to a party at a fraternity that I couldn't go to because I wasn't in one, so if that would bother you that's something to look out for.
Also, I got better at just talking to girls as friends, from talking to her sorority sisters a bunch.Just expect her to be busy and respect things about her sorority and her sisters. The fact is that the girls are shopping for a socially desirable future mate with a probable good future income.