Trying, good for you for realizing those are already muddy waters. My mom never badmouthed my dad and I am very grateful, I have too many issues with him as it is.
It should be very difficult to see reality versus the dream you had about his dad, to me it would be heart breaking but remember you have nothing to do there and your son will always know who was really there for him.
Please keep the good work up, protect your son.. then come here and vent all you wish with us.
((hugs))