What could be the reason for homosexuality and how to treat it?

Hello doctor,

I have been with my boyfriend for two years. We have known each other since we were eight years old. We both are now 30. We have been friends for many years before we dated. Recently he left his email open on the computer and I could not stop reading them. Tons of times he emailed people pictures and vulgar messages. Tons of times he got addresses to go have random sex with strangers. He even offered to host at our home where I and the kids live! After reading dozens and dozens of emails I made him go out that night. He admitted to doing this for years even with his prior relationships. I never had a clue. Now he is begging and crying daily for me to take him back saying that he could never go through with the acts he spoke of in the emails, and never did anything physically with all these men. I do not believe him. It physically makes me sick. But he is also asking for me to help him as there is something wrong with him. I believe there is. And he does need psychological help. I want to run from him. I do not want him near my kids. But I feel like I should help him get help.

Please help.

Thank you.