I wasn't trying to say "give up and break up", just trying to offer a differing viewpoint.
I think your wife has been honest about the way she feels and what she's comfortable with or not at this point, and in my opinion it's better than if she pretended she was fine with in when she actually wasn't.
I think I differ from a lot of people by thinking that sometimes, staying together is bad for a relationship, and people are likely to stay n relationship past their expiration date and make things worse.
This being said, it's true that four days isn't much at all. I hope you guys get better, but I'm not sure what to suggest as I don't know your wife. I'm not sure what would get her to trust you, I expect your opening to her was a shocking experience for her and it's going to be harder for her to trust you than before, even though you've proven more trustworthy than you used to be (since you were honest instead of hiding it some more).
Maybe in time she'll understand that since you were honest with her, there is no reason for her to think you're going to go behind her back. That would be more likely of someone who did not admit they can develop feelings for others.
I understand that you don't want your son to go through that, of course. I was just saying that it's likely to be an empty threat from your wife and that I wouldn't take it at face value, but more try and understand what prompted her to say that. Maybe she felt you took something important from her and she wanted to get you back by doing the same and taking your son away (or threaten to do so) for instance.
I'm not sure how the roommate idea might work. I've known people for whom it worked, but they didn't love each other anymore and were friends more than anything.
By the way, her daughter reacted terribly when she learned they had stayed together for her sake.
I think it might be easier to be honest with your kid right away than have them learn in retrospect that because of him, you had to keep living together for years. Then again, I guess it depends on your kid, but I'm usually on the side of honesty. Things get figured out at some point and it's that much worse when you realise you've been lied to for years.