it's all pre-meditated, if JM can prove this then it's in the bag. She truly is evil and IMO would commit murder again.
I'm betting she told him "if you take this other broad to Cancun...it's over between us" and he probably said "ok, then it's over. peace out". She would not take that as the end, plus add in those texts where he called her a sociopath and etc.She probably went there without any warning and convinced him into "one last sexual fling before we end this for good". They did the deed and she acted like she was leaving, brought her things to the car and retrieved the weapons. Went into the bathroom while he showered to say bye and then she did it, caught him while he was vulnerable. Or.....she may have brought one of the weapons out in front of him and threatened to kill herself if he didn't change his mind on ending the relationship and change his mind on taking Mimi to Cancun. Most likely he just continued showering while she snapped pics and begged him not to end it, he didn't respond to her threats because he thought she was just being an over dramatic witch. He probably though she'd get the point eventually and just leave, but she couldn't just let him go that easily.