Heterosexism

Heterosexism is the belief that only men and women should have sex, or that only men and women should love each other as more than a friend or family member. It is also the belief that sex and love between men and women is better than other types of sex and love. Heterosexism is not just something a single person can believe but is taught by society and culture. Heterosexist beliefs can cause people to act unfairly towards people who are gay, lesbian, bisexual, or asexual.
Heterosexism is related to homophobia and biphobia in the same way that sexism is related to misogyny and transphobia.