He is NOT going to admit the truth unless forced. And even then he will confirm as little as he can get away with.
I wrote this recently on another thread and think it applies here too!
"I didn't do ANYTHING"
"well, ok, since you've got the phone bill, I admit I spoke to her, but nothing else, I swear on the kids lives"
"Ah, you've found the hotel bill, well, ok, we shared a room that one night the bill is for - but I swear on the kids lives we didn't sleep together"
"oh, you've found the empty condom wrapper. Well, ok, we slept together once, - how many wrappers did you find? yes, just the once and I didn't enjoy it, in fact she MADE me do it, I was thinking of you the whole time"
"oh, you hired someone to follow me and you've got pictures, well, she trapped me into it, I have been going crazy with the guilt, it never would have happened if you'd had sex more/looked better/lost weight/paid more attention to me"
etc
etc
etc