Hi Honey, I'm so very sorry you find yourself here, but it's the best place to be under the circumstances.
Yes, it's a devastating journey you're now on, one that you didn't choose, didn't get consulted on, didn't expect in a million years, but here you are.
I'm so sorry you had to hear those words from your WS, they become etched into your brain, very hard to push them away, for some of us they never leave.
I encourage you to read, read, read, knowledge is power, strength is attractive. There's a wealth of information in the Healing Library, (top left hand corner of the page), and read as many of others posts as you can. There are some great ones, usually to be found in the first few pages of JFO as us oldies keep bumping them forward for the newly betrayed (many have a red dot).
There's almost always someone else dealing with the same of a very similar situation. Affairs, WS, and OW/OM generally all have a depressing sameness, same damaging words, same lame excuses, same messed up logic...
Just remember that none of this is your fault, there's nothing you did or didn't do that lead you here, it's all on your WS, 100%. If he was experiencing any issues in life (hell, who isn't!!) there are many things he could have done rather than the most destructive of all, an A.
Take time to think about what you would like going forward, and there's no big hurry. First you need to exercise some self care, make sure you're eating, sleeping and staying hydrated, I'd caution against alcohol, it just doesn't really help. Many of us experience a knee-jerk reaction initially, thinking we have to do the hard work to win the WS back, but this is simply not the case. What happens going forward is up to you, remember that. For many of us, an A is a total deal-breaker, and there's nothing wrong with that, someone else's broken moral compass doesn't have to be a life sentence for the betrayed.
In any case, IC for you is pretty much essential, you need some professional and unbiased support to work through your thoughts and plans. He also needs IC to work out how the hell he let this happen.... and he did let this happen.... it never "just happens"... they never "don't go looking for it"... you were in the same marriage, you didn't cheat. MC would be for some time in the future, should you decide to offer him a chance at reconciliation.
Please, I know this is painful, if you haven't already done it, get yourself along to your DR and have a complete panel of STD tests done, including HIV and Hepatitis C, you will be treated with care and respect, this is not of your doing, you're just dealing with the collateral damage. Do not, for one minute, believe him if he says you don't need to, that they used protection. First off, condoms really only prevent pregnancy, (and not too well at that) and STD's can still be transferred even then. Also, WS who cheat and lie, cheat and lie.... so believe little of what he says at this stage, especially as he's still in the FOG.
There's a post, by Katherine41, 20/20 Hindsight - What I should have Done When I JFO, I'll find it and bump it for you, look for it on this page. Invaluable help for those whose WS is flapping about like a fish on the sand, please don't fall into the "pick me, pick me" trap, it's soul destroying. Your WS should be on his knees, a dribbling, snotty mess offering anything for you to even give R a thought.... Please don't let yourself be damaged further by taking any part in his you/her mess, you deserve better than that, you're his wife.
Hugs honey, I know these are dark days, the best thing I can tell you is that it will get better, you will feel better than you do right now, but it does take time, and some tough decisions. Keep posting, it really does help.
ETD: just read your update, YES... go to a lawyer, don't be afraid, he's probably more concerned about this getting out in the real world than anything else, and please... still get checked for std's... cheaters lie, and lie and lie, minimize and deflect.... please expect the worst and hope for the best, protect yourself.