might be less that he's a mommy's boy and more that after realizing killing han didn't make him stronger but left a hole inside him, he doesn't know what killing his mom would do to him
btw, i was watching while crying internally because carrie fisher especially the goodbyes with holdo and the last luke leia moment. If not bcos my kid staring at me and not really looking forward at explaining why mommy is crying, there would be ugly cry
mine was: so clearly, you should have just sent Leia to Kylo in the first place