NTA. And oh the irony... Did the guy sleep through the class? Cause he definitely has misunderstood the meanings of Society and the diversities society involves.
He was rude and hurt your feelings. You have every right to feel the way you feel and you acted right by asking to change seats. Time for the guy to learn that some topics are not socially acceptable as jokes. Cuddos to you for standing up for yourself. Stick to real friends that accept you as you are without judging things like your sexual orientation.