((emotionalhell)) Well if your reg date is any indication of your D-day then you have just experienced it.
R cannot be achieved if your partner is not willing to man up/own up/do the work.
You asked the question: Why should I stay with someone who can't own their own shit?
Why would you? Because your son opens up around him? Because you don't feel people will tell the truth? Because your ex won't be around for your son? That is not enough.
This man will hurt you and your son down the road (he already has) if he cannot own his behavior now. Read the Healing Library. Do the 180.
What kind of role model is he for your son? How will your son view you in the long run?
I highly recommend you look into IC and put the wedding on hold for at least one year - until you are sure of yourself and can better trust him.