Bman - welcome to the boards. I feel uniquely qualified to provide you with some advice because our situations are so very very similar.
You can read all about mine if you like, but I have the same sitch as you. I've been married for 4 years, met my W in college just like you, became inseperable since meeting and we have a 4 year old son together.
My W gave the same speech as yours, except there was an EA involved. From what you describe, your wife is more than likely involved with OM. I'm sorry to say that, but all the evidence and my gut feeling looks to that direction. In my case, when confronted with evidence my W stopped after several attempts went no contact with the OM.
If you want this to work, you have to begin by doing some real giving and keeping up with your 180s. Start GAL and doing things without being asked. Like you, my W did most of the caretaking of our child during his first 1-2 years and she built up resentment for me for that as well.
You can't change what has happened or even how she feels. It is how she feels. You can only give her a better version of who you are, and a better option than a D.
She will need space. The biggest mistake you can make right now is pursuing her and not giving her that space. You MUST give her that space if you want your M to survive. This is NO LONGER ABOUT YOU AND HOW YOU FEEL. Get that. through. your. head. It is no longer about you. It's about how you react to her actions and words.
Start by validating everything she says. Do not argue. If she says that she wants a separation, agree with it... "I think you may be right that a separation is the best thing for us right now." It may seem like you're going full steam ahead towards a D, but you are not. When you don't argue with someone the lose the motivation to rebel against you. I don't know how old you are, but this could very well be your W rebelling against you because you met young and married young. The longer you put up a fight, the higher the walls she will build against you.
The first step for you now is to validate. The second step is to 180. The third step is to begin REAL GIVING to her. Fulfill her emotional needs. Are you familiar with the Five Love Languages (LL)? What are hers? It sounds like Quality Time and Acts of Service are what hers are though I can't be certain. Those are at least what my W wanted that I did not provide.
When you do real giving, you do it with no strings attached. You do it because you value your W and love her.
Even if she is in an affair or there is an OM, if you fulfill her emotional needs there will be no need for her to reach out to someone else. But, at the same time you have to expect that she will NOT fulfill any of yours. It is hard work.
We get it here. You love your W. You want to save this M. We all do. But, there are steps you MUST take if you want that happen and they will not be easy. Consequently, they'll be the hardest steps you've ever taken in your life.
Doing something that doesn't come natural is a higher version of love. Remember that.
----"Et tu, Brute?"---- me:28 W:24 S4 T:6 M:4 EA Exposed: 5/21/10 Bomb: 6/20/10 (Father's Day) NC w/ OM: 7/10/10 W moved out 8/21/10 http://bit.ly/aOrZne - My sitch