Sexuality is fluid, meaning that different people have varying sexualities. To clarify, a person can be exclusively heterosexual or exclusively homosexual. And in between, bisexual persons share feelings of both.
If a person has sex with a person of the same sex, doesn't that make them gay?
Not necessarily. Sexual orientation is a feeling, attraction, or "self-concept." The American Psychological Association goes on to explain that "individuals may or may not express their sexual orientation in their behaviors."