How can I tell if I'm sexually oriented to people of the opposite sex?

Think about what people get you aroused and what gender they are. This doesn't necessarily guarantee anything, but which gender do you fantasize the most about (although there are heterosexual people who do have homosexual fantasies sometimes so it's okay)? Also try to think about what which gender you feel more attracted to (if you feel equally attracted to both, then that could mean you're bisexual).