Any characteristic that is relatable can be part of your identity. Or, put another way, any differences between you and another person which makes your emotional responses different can be part of your identity.

People who can relate around a subject can form a group identity. If a person in a group has a different base reaction to the rest of the group (and especially if the reactions are incompatible, unaccepting of each other), the person can feel outside of the group. They will not identify with the group.

Sexuality is definitely part of a person's identity. Emotional responses to sex/sexuality are quite involuntary after all.