There is a trivial question that I could never answer. That is why some people can only have a long term relationship/ friendship with only one gender. For example, there is this person (female) who I know that can only be good friend with guys. She can never make a long term and meaningful relationship with women. As soon as, she gets too close something would happen to split her with those female friends. I have some hypothesis but I am wondering if there is anyone out there with a good explanation as why this happens.