So if this is his third child then it's likely a planned child. Of course he never stopped sleeping with his wife. It's typical cheaters excuse: not sleeping with her or not loving her. Yeah ok.

He pretty much just had a mistress for two years, at no point though he wasn't intimate with his wife. He likely just wanted to spice his life with side sex. Gross. Not a decent man.

Do you really want a best friend who thinks it's ok to take on a mistress and cheat on his wife and lie for years!!!

Be done with him and seek therapy for figuring out why you thought it was a good idea. Hope you can heal soon and find available man. You can do it. Stay strong but completely cut contact with him