I think it is only natural for sororities to hang out with one or two fraternities most of the time - that's where most of your sisters are so that's where you will hang out. I know that in my sorority, it was pretty evenly divided between XYZ and ABC "groupies." That of course changed from year to year.
However we always tried to mix with every fraternity (there were 10, if I remember) at least once a year and not exclude anyone. But there was one sorority on campus who wouldn't mix with certain fraternities, and could only date the "better" fraternities, football players, etc.....Basically the guys who they labeled as "not good enough" just saw them for being the stuck-up jerks they were and moved on.
If it has really gotten bad, approach IFC and Panhellenic about setting up a mixer schedule (I am assuming your social chairs do it now) so everyone gets to at least meet everyone. It might not completely solve the problem but it may help to dispell some misconceptions. Also, if there are several small fraternities, two of you get together and have a mixer. Speaking as a female, it does suck to come to a mixer when there are 40 chicks and 20 guys.
