I think you've got the right idea today. I wish others were here to give advice. You're right to try to avoid analyzing the text message; it's positive, and it's probably best to leave it at that. There will be a tendency to look for the fourth layer of hidden meaning beneath everything she does, and even when she does have motives below the surface, it gets exhausting for her to deal with the constant analysis of her every move. It's perfectly understandable why we do it, but it still pushes them away.
Your focus on your son is the right thing to do. Even if the marriage ended, he would still be there and still need you, and you have a lot of control over how this whole process affects him. Secondarily, it's a good distraction to keep you from obsessing over your wife. We do it because we love them, but again, it pushes them away. You have to be able to focus on yourself and your son and let her figure out what she wants.
You will backslide again, but as long as you get up and keep going you'll be OK in the end. Keep at it and do the best you can.
