Quote: he cut me off and said "Yes it is your business"
Here you are, at the place I was a few weeks back and it was at this point it occurred to me to be direct (thanks as always OT) and just come out and ask my W if she was saying we were now at a point where honesty was expected from both of us. She said yes, and immediately I changed my approach to just start giving her the benefit of the doubt most of the time instead of thinking the worst. I told her it was important to me to know that she CARED if I trusted her because it seemed like for the longest time, even before all this, it didn't seem like she did. She said she did care but sometimes felt that no matter what she said or did that I would not trust her so why try. This was important too because I got to let her know that I COULD trust her if that's what she wanted (she said she did) and I would work towards that starting right then.
Again, to me, it was VERY important that she tell me she wanted my trust because then it was easier to understand some of the things she did or said.
I know that was all about me but I hope it applies to your sitch.
I think SO could do a lot for you in trusting him but maybe you need to ask him directly if he can be trusted and more than that if HE wants your trust. Someone bent on lying and continuing an affair would not probably want your trust, they would likely just avoid the conversation. That's what my W did for a LONG time.