How to balance if your SO thinks you kiss the a** of your parent/s?

My situation:
Live-in bf thinks I kiss ass to my live-in mother. He and mom get on well but he thinks I let her walk all over me while “giving him hell” and he wants to know why mom gets the special deference?

My response has been because my mom is right so often about anything (I’m not) and because she does so much for us as couple then I do feel to give way to her if she’s a little snippy or demanding.

Why I don’t kiss his ass is because I don’t want to sidestep him, he’s my partner and I want to take the time with him to compromise, learn ways to do things together, carefully and not to just “not rock the boat”. I’ve never gotten on with my mom but I do respect her. To me it seems okay to treat them differently, to invest in them differently.

What say all of you? I know it’s a long read