I'm so sorry to read of your situation but you are with great company here, keeping reading and posting!
If you need to vent or have a good cry, do it here or with a trusted friend or family member. Part of your healing comes from detaching from your wife and part of that means not engaging in emotionally intense (and currently fruitless) conversations. Showing a strong confident you will have a bigger effect on your wife than any of the crying, pleading and begging behaviours most of us do at the start! It will also help your emotional and mental state once you start "making" yourself act like that.
Just a quick observation, but in your state is your wife allowed to take your son so far away without your consent? MakingChanges made a very salient point about being involved in your son's life, I think you should be very calm but very assertive about the living arrangements concerning your son.
Her comment about you moving house to be nearer her sounds like typical selfish unfaithful spouse fantasy script. Do you want 50/50 custody now? Given the physical distance between you and your wife right now maybe a weekly rotation would be the most feasible and certainly fairer than the current set up. I'm sure your wife won't like it but tough, if she wants the separate life then losing her son part of the time is part of that price. Besides, why should you lose out on your son on top of everything else you are going through? Why should he lose out on his father?
In your position (and I was there 10 months ago..) I would drop all relationship conversations, show her only you being strong and calm, even when you feel like cr@p on the inside (trust me, this gets easier with time). Be polite and respecful but don't be a doormat. Be civil and friendly but certainly not her friend. Now is not the time to give her any emotional support given her affair, bailing on the marriage and taking your child. She wants to be without you? Show her what it will be like.
Make getting your son more often your number 1 priority and make re-connecting with yourself and others who love and support you you number 2 mission. Keep busy trying to do things you enjoy doing, take your son out on more trips. Remember this isn't all about you. Just because she is treating you awfully doesn't mean at all that you deserve it and you are somehow a lesser being. This is another part of detaching, no longer being defined by how another treats you, needing validation or support to "complete" you (as Dr Evil would say..).
I now this tough, this is hell right now but, certainly for me, once I stopped engaging in emotion led behaviours and actively worked on myself and detaching from wife things got better.
Take care my friend and take care of your little boy, he needs you more than ever right now.
Scotsman
Me - LBS 47yrs old Her - WAW 34yrs old DD - 10yrs old Together - 15 months Bomb - 28/07/15 "I still love you but can't deal with situation"