Mocking your stammer is pretty severe, but I guess if he is nice to you in all other aspects then maybe he’s just unaware of how inevitably big of a part it is of your life. Also, about your mom being worse, just out of interest what does she do/say to you? obviously you know a lot, lot better than me about both of them, but I’m guessing that she took care of you throughout your childhood, and someone being nice to you on a one off is different to being nice to you on a daily basis. Idk if you get what I’m trying to say.