My Ob/gyn clerkship director went to Columbia and he is gay, and a guy from Tufts who is gay just started his internship at Columbia in Ob/Gyn as well (I think he's single too, I'm perhaps falsely assuming that you're male, but if you are, keep an eye out!). From what I hear (albeit rumor mill), Columbia is very diverse and "gay friendly", hope you have a great time!