That said, he may have other intentions as well that are yet to be revealed, he is also someone the story has presented as good at hiding his real feelings.

I think it's largely a sense of control. He's been lied to, manipulated and felt inferior for so long at true cross that he is lashing out for a sense of agency, and whether logical or not, his desperation for agency in his own life is leading to extreme and seemingly illogical action.

If his body wasn't rotting away, I'm sure Lucifer would have been doing a happy dance to see Memphisto take one to the face.