Megs are you sure you have no chance of winning custody? In California the biological parents keep rights and can fight for them. Especially with these types of circumstances. It may be worth speaking confidentially to a family law attorney just to make sure. If not custody then maybe regular visitation rights?
I'm so glad that you have made it so far. Try not to look back at what you coulda or shoulda...it will only tear you down.
You did the best that you could, period. Forgive yourself and look ahead.
You are a true survivor.