I guess that most people discover that they can be attracted by the same sex at a later age when they are already married or in relation.
I also think that this curiousity grows bit by bit and the first experience will probably happen without the partner. I dont know if there are more bisexual women than men? I think many men dont tell about it but enjoy a lot when they meet a couple with their wife to see the other male and friction with him and maybe sometimes mutually suck eachother while the bi women are enjoying.... In fact once people becoming elder the way they experience their sexuality changes a lot... and one of the changes is the feeling and enjoyment of tenderness with same sex or opposite sex doesnt matter so much anymore....
