Man, you will get a LOT of argument over the answer to your question!
My opinion is nobody is born with predetermined sexual tendencies; rather, they are influenced by their environment. Primarily through family, but there can be interactions with other adults that can have an affect. Especially if it involves abuse.
The way I see it, bi or gay sex begins with natural curiosity. Of course, some guys are more attracted to that idea than others, just as there will be many different responses/reactions. Guys that find the sexual excitement of bi/gay sex to be as much, or more, satisfying than any other sex will tend to adopt more of a gay lifestyle or tend to have more frequency.
Guys that enjoy for what it is may find it exciting/fulfilling enough to have some desire to do it again, but save it for a "special occasion" event, as opposed to seeking it frequently.
That's how it was for me, but everybody is different.