It is what it is.
Acceptance is one of the recognized stages of
Grieving a Relationship Loss.
You mentioned he was on a smear campaign at first. In that case you need to be doubly sure you're not improperly blocking any parenting available to him. No, you don't have to push visits on him, you don't even have to remind him to visit - and you shouldn't - just be sure you don't
block them. Just follow the order.
It's possible those first few months were his
overreaction, something typical with PDs. Maybe now since time has passed he's reverted to his baseline level of contact? Be aware that thre can still be occasional exceptions such as at holiday times.
For example, my ex is a very possessive mother, she would never drift away. However, some mothers do, though not many it seems. It's apparently easier for a father to drift away and society is okay with that. If he drifts away, so be it. Don't try to live his life.
In short, don't guilt yourself about him. His life is his life, his choices, don't take responsibility for him. You do the right things, follow the order and you won't have any reason to feel obligated or guilted.
F.O.G. = Fear, Obligation, Guilt