I was married less then 4 years, now my ex is living as a gay man can I sue him

Sue him for what? You call him your ex, so I assume you are already divorced. How are you damaged?

Sue him for divorce, guy people do marry, many "gay" may be :"bi". You can not sue him for anything extra for being gay.

My ex is now telling his family he knew he was "gay" in high school is now 56 years old. And he use me just to have children.

And most likely he did, and there is nothing about that, you can sue for, you can have his family testify at your divorce hearing to try and get a better settlement, but that is about it.

If he is with someone in particular, some states still have the right of action for "alienation of affections", in theory.