>>150450506
did Mike suddenly turn on Lucy during December because she hit him?
Or because he was reminded of her violence?
Nope, he very quickly 180'd because Sandy called and he remembered he had to push away the "problem"

This was Mike's motive because he admits to it, or if you want to establish a second motive then it's so she could also feel as alone as he was (because he isolated himself for a phone)
Notice the first thing Mike says in his defense to Sandy is about how Lucy isn't getting between them anymore, I suspect the next few pages are going to confirm what was basically already fact.