Dan wrote me an email and very respectfully inquired as to what halakhic basis I have to be friends with guys. He pointed me to Igros Moshe Even HaEzer Part 4 Siman 60. You can see it below.
R' Moshe Feinstein on Platonic Relationships
I read the Igros Moshe and entirely see R' Moshe Feinstein's point. There is no question that when a girl and a guy become very close to each other and intimate in their language and behavior that can lead to engaging in things that are forbidden, even if this was never their intention. Is this enough of a reason to forbid all relationships between men and women until such time that the two are of marriageable age? I don't think so. But can I find a place in halakha where it explicitly states that my friendships with men are totally permissible? I am not sure.
I believe with all my heart that it is entirely possible for men and women to be friends at the intellectual level without that leading to anything more. I think it is the exception rather than the norm that it would lead to something beyond that. But it is also possible that I speak only for myself, and even if I do not agree, I will admit that I see where, based on this Igros Moshe, people are coming from. The Shulchan Aruch and the Rambam's subsequent points I cannot entirely credit seeing as I'd like to meet the man who beats his wife (Rambam said he could) or the brother who doesn't kiss his sisters before I take that at face value. But R' Feinstein? I hear. I don't agree, I cannot agree, but I do see the basis in halakha of those who forbid these friendships, even if I think the way this has been practiced nowadays is very flawed. It would be much better to teach boys and girls to interact respectfully from their youth than cage them away from one another lest they fall to temptation. There is much that is lost in the non-coed classroom and a million things you miss if you've never been friends with someone of the opposite gender. Nonetheless! I see the Igros Moshe; I see your source.