I would believe that people aren't born gay but choose to be gay based on their surroundings and the place where they grew up.
"The art of war teaches us to rely not on the likelihood of the enemy's not coming, but on our own readiness to receive him; not on the chance of his not attacking, but rather on the fact that we have made our position unassailable." -- Sun Tzu, The Art of War
Is something in mind considered biological? If so I would say biological. I think some people are just wired that way.