This sounds like a miserable way to live.
You could choose gratitude for a good man, aim to love him and relish the lovely family unit you have together to provide for your child.
But I think it sounds like the chances of you doing that are zero.
You've been prevaricating for 18years, talking endlessly about it, torturing him with your indecision while you ponder your own emotional state endlessly for years.
Leave him. Be miserable and self absorbed on your own.
Or choose to actively love what you have. Not what you wished for, but the reality of the good things life has brought you. Put this good man and your child above your own endless emotional temperature taking and devote yourself to the people in life who love you and need you.
Shifting focus outside yourself to a greater purpose is one of the best things for depression. I
But it sounds like you won't choose that. After 18 years you're still wondering about how you feel and all your own personality quirks that mean you just can't commit.
If only you'd got just what you wanted, instead of just a wonderful man and a child, what to do??
So leave. Spend the next 20 years experimenting with dating to find your true love, and discussing it endlessly with a therapist. But go and live out your self absorbtion on your own instead of painfully playing with this 'wonderful' man.