J.M.
I am just starting potty training with my son so I don't have serious experience related advice but while I realize this is very frustrating, I think you need to take a step back and put it in perspective. He's fine, you are fine, everything is fine...he's just exhibiting a difficult behavior. Stressing out yourself, or stressing him out--making a big deal about it will only make it worse and cause an actual psychological issue around it.
I mean, your son's poo habits should't be detrimental to your marriage ;-) Yeesh, with that kind of pressure it's doubtful *I* could perform!
It does kind of sound to me like he might have a control issue regarding his pooping so offer him this: poo in the big or little potty, choose one. See if that works...if not, put him in pull-ups and address it again a week. So, he's spending a bit more time in the 2 year old room. I understand that is upsetting, but really he's going to come around in his own time and once he does you can put this behind you. In other words, ultimately, the only thing YOU have control over is how you choose to deal with the issue.