As his own father said, things were not going well for WRE for the last few months. Before meeting and/or hooking up with LL, he appeared to have it pretty good. A new father, perhaps living with his ex and his children? In the months that he was with her he lost his job, got busted for drugs, got evicted, had to move into a bedroom with her and her kids, out of town and away from her family who may have babysat, got into some violent issues with his ex and her family, was charged...getting an injunction against seeing his own kids.
That night, he didn't want LL to go to work. IMO he was basically fed up with everything LL and her children stood for as well as playing babysitter and he took it out on a fussy baby. His comments about how much "in love" they were are a cover IMO as well. He probably had a growing resentment for her and her children.
MOO