Why does he have to be so mean

So I’ve been with my bf for 6 years, he came into mine and my sons lives when my son was 2 so he’s really the only “father figure” my son has ever known since his bio dad left when he was a baby. We have lived together for 5 years and we have a one year old daughter together. I’ve noticed now that my son is older my bf is mean to him, but not in like an abusive way it’s more of a rude or teasing way. It’s starting to give me anxiety as my son as been telling me he doesn’t think my bf likes him anymore. He also refers to my bf as his dad because that’s all he’s ever know so you can imagine how heartbreaking it is for my son when my bf acts like a jerk to him. I understand my son is very strong willed, doesn’t listen to well, can act quite selfish and entitled, and complains a lot but what child isn’t like that? But that’s still no excuse to be mean. Today we were out for a walk and we were talking about donating stuff to good will, my son was complaining about the bugs outside and my bf made a comment that we should give my son to good will as well because he complains too much. I couldn’t believe he actually said something so incredibly mean, I could see my son tearing up and it broke my heart. I don’t know why my bf has turned into such a jerk lately but it’s stressing me out. He’s also not as nice to me as he used to be, he tends to always talk down to me or treat me like a child rather than his gf. He’s amazing to our daughter tho. I need to talk to him about all this but he gets really defensive whenever I call him out on things and I am a very emotional person who often cries when trying to voice what’s bothering me.

Has anyone else here been in a similar situation?

I get that maybe my sons behaviour annoys my bf, heck it annoys the hell out of me too but I would never ever say anything to hurt his feelings, that’s just a childish thing to do especially when your the parent and your child looks up to you.

I told my son that the next time my bf says something that makes him feel sad he should immediate speak up and tell him that what he is saying hurts his feelings and makes him feel like he’s not loved. My son told me that if he said that my bf wouldn’t even care, this broke my heart too but I told him say it anyway, make sure he knows that he’s hurting your feelings. I just don’t get why he’s like this, I’m starting to feel less and less happy in this relationship and it’s a horrible feeling. We love his family’s and they have accepted us as their own, and aside from his jerk personality he’s always been there for us and he has other amazing traits. He used to be so nice and that’s what confuses me.