First off - he is blaming you, but he has no-one to blame but himself. But since the child is living with you, rather than acknowledge his own contribution in his son's dis-acknowledgement of him, it is easier and much more convenient to blame you. Do not take it to heart or even take it personally. Ensure at all times that you do not bad-mouth him with your son, never telling him the real reason he doesn't see his daddy (daddy's working hard, or some sort of excuse), always ensuring him that his dad loves him very much, and you don't need to feel guilty of anything. Don't force him to talk to his dad if he flat out refuses. The father must find a way to reach his son again, not you. Stay neutral, keeping the child first. It will work itself out.