Having children leave the house is a re-defining moment, just like establishing a family in the first place. It's scary, but it comes with all kinds of possibilities as well.
It sounds like you did a good job on reinventing yourself as a parent, of course trusting your judgment that your kid is indeed wonderful. But the fact that you love him enough that it keeps you going probably counts as further evidence that you're not doing so bad.
You'll manage to reinvent yourself again. And if you can't do it in your marriage, there's no shame in doing it outside it.