Don't absent parents suck? My oldest son's father is like yours, but at least mine had the decency to move out of state and not bother with contact. Out of sight, out of mind.
I would be very tempted to stop play miss nicey-nice and tell him that because he hasn't been able to maintain regular contact with your son, he won't be seeing him again. If he has court ordered child support, push for enforcement but make him fight you for visitation and then only comply as much as the law requires. I would certainly do this man no favors.
Protect your son's heart as much as you can - don't tell him about expected visits in case his father is a no-show. Cut communication off so that he doesn't have the chance to tease him with the thought of a visit that doesn't happen. Yes it will suck for your son, but who needs to be rejected and ignored repeatedly?
My SD's absentee mother does the same BS only in a way it's worse because they lived together until a year ago and she is old enough that her mom calls or texts her directly, talks a good game about how great her life is (gee it must be great to abandon all of your kids and move in with your new boyfriend and his kid) and then falls off the face of the earth for weeks or months before popping up again to wreak havoc.
Perhaps some counseling for you and your son would be helpful - you can both learn to deal with the rejection and cope with the irresponsible father as best you can.
@Robin FWIW I read the "he hates him" comments differently and that it's the son say that he hates is bio father and wants nothing to do with his bio father. Can you blame him? Kids can definitely articulate feelings like that all on their own.