My boyfriend is weird about God chats

Okay so my boyfriend is Muslim and I’m Christian and my mom always debates with him about God and he’s always chill with it. My older brother just came home for the holidays and they got in to a God debate and afterwards my boyfriend told me how that was so stressful and overwhelming and avoids my brother now. It bothers me so much, and I don’t know why he gets stressed about one of them and not the other