Maybe that is true, he may have ended up cheating when you were married with kids instesd. He is a cheater, you found out now, that is good. Everything else is pretty bad...

It isn't about competing with men, he is likely bisexual. He may still love you; he just also loves this man and doesn't know how to handle that.

That, however, is his problem, not yours. You have been wronged and deserve better. Your trust has been breached and communication has not been respected, what he did is not ok.

Confront him however you need. You can be angry, you can be hurt, you can be confused, any of that is valid; just get closure and make your choice accordingly afterwards.