father is not coming

That's really unfortunate.
I'd just let it go as it is.....
The little guy doesn't understand it yet, and if the dad doesn't say anything now but does later, you can still explain it to your son.

Best regards

this sounds more like an attachment issue. Was there a lot of tension in your family while you were still together/during your pregnancy? And even in your belly, your child picks up on these feelings. Actually, your child feels exactly how you feel at that moment. So maybe your child associates his father with stress and remembers how you all felt when your ex was at home. If your ex has had little interaction with your child since birth, that feeling can only be reinforced. A baby is extremely focused on the mother; you are the most important person. A baby can only feel; they don't have words for it yet. What they can do is cry. Through crying, they can let you know how they're doing. Your new boyfriend does take care of your child, so he can form a good attachment with your boyfriend. Sad situation, but is it the lack of a father that makes him "lose" his own son to your current boyfriend? And honestly, I would leave it as is. If he wants contact with his son, I would allow it because personally, I don't think a child should be kept away from their father no matter what happens between the parents. But getting a good bond with his child will still be difficult for him, I'm afraid