A couple of thoughts....
My reco is to do nothing with M assets before you get good legal advice. For example, my son was advised NOT to withdraw funds from the joint account. IIRC, he was also told not to move out of his M apartment at all, when he and his STXW were talking about taking care of their son on alternate weeks. (I guess the idea was to rent another apartment and each would live there while the other did child cae. Son's D lawyer advised against doing that.)
The only legitimate legal advice anyone on SI can give is: talk with a good lawyer who knows your jurisdiction's laws inside and out.
*****
Only some 'experts' recommend staying away from sexual details. Our MC recommended asking any question I wanted to ask, as long as I remained aware I might be haunted by the answer forever. At first, I asked any question that jumped into my head. Eventually (weeks?) I asked myself why I wanted to ask a specific question.
That is, I asked questions if I really wanted the answer. I refrained from asking many Qs, though, because I realized I had ulterior motives. For example, often questions occurred to me when I was angry. At those times, it was way more healing to express my anger directly than to ask a nasty question.
I would cheat only for sublime sex with a goddess, and maybe not even then. I assumed my W was cheating for sublime sex. She wasn't - my W said it was mundane, except for the first few times, and ow's sexual demands became a burden. That was hard to believe at first, but her answers to questions, comments, and behavior showed she told the truth, IMO.
In most cases that people have written about on SI, the sex with the ap was different or worse than with the BS, though that's not universal. Your W, if she's having sex with this guy, looks like she's in a phase in which she wants him and thinks the sex is great, and maybe it is.
I'm not sure the quality of the sex matters much to the BS. If they are truly unhappy with the M sex, they're as much to blame as the BS is. If they wanted something different, it was up to them to ask for it.
The fact is that a WS who had sex with an ap violated the M, whether the sex was good, bad, or indifferent.
*****
Q & A has a number of outcomes. Coming clean results in helping both partners heal. It helps rebuild bonds. It helps rebuild an M based on honesty, on recognizing and resolving issues, rebuilding trust....
Not admitting the truth tells the BS that the WS isn't honest and therefore isn't a good candidate for R. That's a devastating outcome, but as Bigger points out, the sooner you learn this, the better for you.
I know you're hurting both from your W's betrayal and by her behavior now, after her betrayal has come to light. Just ... have some faith in yourself and in your future. You're recognizing where you are. You're preparing yourself to maintain boundaries and to to D. You are setting your stage for healing. It's hard work, but the payoff makes it worth the effort.
*****
And they ALWAYS Affair down. Always: https://survivinginfidelity.com/topics/558762/honey-they-always-affair-down/
[This message edited by SI Staff at 5:13 PM, Thursday, January 12th]