You're a dick friend, who did a dick thing and all you care about is yourself... honestly, you say you're scared how he'd react or what would hapen to your friendship... it isn't about you. You fucked is wife, how about doing him a solid for once and coming clean. You've been selfish enough, think about him for once, what he decides to do about you and your friendship should be up to him. it's not the fucking truman show, be honest let him decide, it's not your choice to decide what would be best for him... what happens down the track when he finds out later on, has kids (might not be his) etc etc.