Because you will lose your son if you leave. And statistically speaking, chances are his life won't be a great one.

I don't care what's "best" for you. You decided to marry this person and you had a child with her. That was the choice you made. I care what's best for your kid. And he has no choice. I think if he did he would choose to have a caring father with him, rather then a series of "dads," and the statistical chance one may be a child molestor. There are men that look for women like your wife (needy and desperate) for that reason.

And then when your child is 17 (and you've had all those great years with him to watch him grow, and be there every night with him helping with homework, volunteering to help with his sports teams and being the one person he knows he can count on forever), then file for D and kick her to the street.

There is no arriving, ever. It is all a continual becoming.