I don't think they can just be friends. Aquaintances, yes. But hangin out every weekend or something like that, no. I've seen it first hand with my first girl friend. As soon as we broke up, she banged one of her friends. She told me.
Ok, hanging out EVERY weekend (to the point it's excluding one's S.O.) no, that doesn't work for anyone involved. But hanging out socially, riding, etc... (both as a group, and with respective S.O.s and others, etc....) why not?
Sure, we've all had bad relationship experiences in the past, but why punish the person in your life for something done to you by someone in the past?
Personally I couldn't just be friends with a girl. Every time I have been a friend with a girl, something happened. Not intentionally, but after a while of hangin out with a girl, it just happens...with me anyway. I don't have any girl friends. Mostly just an aquaintance.
Hmmmph... odd. I've always had guy friends (I mean, seriously since I was like 3, my closest friends have been guys). I have plenty of female friends as well, but, especially being in the sportbike scene (which is male dominated) the people that I enjoy hanging out with and have stuff in common with are predominantly male.
(and for the record, Chris -- the BF -- has no issues with it... he knows there's no reason to be jealous, so it's never even come up as an issue).