I probably worded that wrong. What I meant was my husband would need to stay in the marriage at least until the youngest was 18. After watching the instability and pain that separation and divorce caused the kids, we both agreed that at the very least we'd need to stay married and try to make things work until the kids were out of the house. We couldn't be selfish. It's not "just trying" it's "just doing it." It's making a committment and following through regardless of whatever selfish "feelings" came up. We would have to grow up, compromise, work on being a team, learn to give more, forgive more and be there for the kids... and be supportive and good friends to each other as well.
This doesn't mean I want to leave, or want my husband to leave, after the kids are grown. We both hope to eventually retire and grow old together. But we have a firm and unwavering agreement that we will stay together minimally until then. Hopefully, by that time, the growth, and friendship will be strong enough that we'll want to stay together for the rest of our lives.... And if not, at least we had a great family, good times, bad times, lots of memories.... I won't have any regrets.
Now, how long were you married? Any other marriages? Are the children all from the same marriage? How old are you and your wife?
I think with your son you need to be honest and share your thoughts. Talk about friendship, how people can love each other so much, but also make mistakes. Even adults make mistakes. But he's very important and you'd never want to do anything that would hurt him. Ask questions. Get him to talk and listen, listen, listen!!!
There is no arriving, ever. It is all a continual becoming.