It is terrible to see children suffering and I am no expert because I have always felt useless in regards to fixing it. It is good that you are there to listen to him. Even though what he says sound terrible, maybe don't discourage it in hopes that he will continue to talk about it. Maybe something serious is going on (but maybe not, don't assume either way) and if it is the only way to find out would be to make your grandson comfortable about expressing himself without judgement. He also could be referring to his dad that way because he senses his mom's anger (I don't know if she is angry or not) about his dad. Kids are very protective of their moms sometimes. The fact that you see your grandson 2 or 3 days a week is so important and wonderful. Kids need a lot of love and grandparents definitely "fill in the gaps". I hope things get better for your grandson.