As Nemo, Flooded, and Arcangel have explained, no, one cannot "become" or be "made" gay. Sexual abuse does not change someone's sexual orientation. Abuse is something that happens to both heterosexual and homosexual people and, while it is certainly tramautic and certainly affect those who experience it, it does not have the specific affect of altering their sexual orientation. That is an unfortunate myth and negative stereotype that, I believe, is harmful to spread. It perpetuates the idea that people are only gay because something bad happened to them, which gives the impression that there is something negative about being gay-- which there is not.

To use personal experience to illustrate my point, I'm gay, and I have never been sexually abused. I have dozens of gay friends, none of whom have been sexually abused. I have dozens of straight friends, a few of whom (unfortunately) have been sexually abused. There is no link between sufferring sexual abuse and "becoming" gay. A gay sexual identity is something one is born with. It is something that exists well before the age of 12. I knew consciously that I was gay when I was 5, and I know I was born that way. Most of my friends, gay, bi, and straight, report having attractions at early ages as well, and know that they were also born that way.