It seems all this stuff looks so much better on other people -- marriage, children, jobs, divorce. The reality is not as good as it looks. You can't make her choices for her. But you can be the best choice. A lot of people will say that doesn't work, being the best option. I've seen it work right here on this board.
It takes patience, and commitment, and maturity. It's what my husband did for me, and what I did for him when the shoe was on the other foot. There is an adage, if you love someone, set him/her free. If she loves you, she will come back to you.
There aren't any quick fixes to the situations we find ourselves in, and no guarantees. But you know what you offer -- a home and love and family for your son, something no one else can offer.
Growing up looks so good, but once we enter the adult world, we realize that we had it much better when we were teens and had no responsibility. There is no going back, but there is finding the good in the life that you have. I think both you and your wife can do that. And in just three weeks Retrouvaille will help you.