When a child has had to endure the shock of his mother walking out of his life, he has experienced real distress.
In my view, he should be allowed to have his comfort toy. Eight is not such a big age, and there is no need to impose macho values so early in life. He will definitely outgrow the need and drop his toy, but there is no need to force the pace. Give him tenderness and kindness and use a light touch and a sense of humour when you are giving him rules.
I think a sense of security is essential for the child and when he is smart enough to say that he feels secure when he has the toy, it would be very unkind to deny him that. Do persuade his father to be gentler and affectionate with the child. The child needs to know that some relationships are constant and still predictable.