Father's Day and relationship with son

I've seen a lot of posts about mums asking if they should get their Ex's Father's Day gifts from their young children. Even if these men have been abusive, hardly done anything for children or never wished mum a happy Mother's Day. Most people reply that they do and these mums should also to set an example. My sons father hasn't seen him in two months. Their relationship has always seemed very forced on both of their sides. His fifth birthday has come and gone in this time and it was the first birthday he's missed. Our boy refused to make his father a gift at kindy and when I asked him about it he said he doesn't like his dad. I'm wondering if this is because he noticed he missed his birthday or because his dad has been getting more distant lately. He seems to be suffering severe depression previously diagnosed awhile ago. He hardly leaves the house which he told me. Our son has been getting more distant from his father each visit. Doesn't like to go alone with him or asks to come home early. I've been getting bad vibes from these ocations and honestly don't feel comfortable leaving them alone together anymore. His father has aspergers and is medicated for schitzophrenia. He was violent in his childhood before being medicated. I've never felt unsafe around him but lately from how my son and he is behaving I don't feel comfortable anymore. I don't know if I should encourage their relationship and get his dad a gift with our son or let it go until his dad contacts. I know it sounds bad but our son doesn't seem to care for him. I'm wondering if that's why his dad is getting depressed. Dad's family also seem to be getting distant.