I think it is a choice for some but not for others. I believe this because if you put a group of men together for a long stretch of time and gave them no contact with women, some would end up having sex together whereas some (I include myself in this group) would never resort to homosexuality no matter how long they were away from a women. This can be seen in prisons, at sea and with cowboys in the old west. (There is a film about two gay cowboys out now, apparently homosexuality was quite common among some cowboys because of the long times away from women)

Similarly, as in Columbine's example, some gay men can be the target of desire from amazingly beautiful women and still go for a man.

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It's the difference between suicide and slow capitulation... - Jim Morrison