The desire to remain anonymous is understandable. I feel that I have been let down. Of course you feel betrayed. Try to understand, that not wishing to hurt you, possibly feeling ashamed or embarrassed, he has kept this to himself. He may feel discovery would bring to you both problems.
Transvestites are a secretive lot.
The incidence of homosexuality, or bisexuality,among transvestites is no greater than among the population in general. No, Transvestism is not an illness. It only means that he sometimes has the compulsion to dress as a woman. As we have already established, transvestism is not an illness or disease. It is a departure from what society accepts as normal practice.