Agree with you. Only thing is, I can tell that not being invited to join him for that all-expense-paid trip to Cancun was her trigger. I say it was this trip, not simply that he was seeing someone else because:
1. When things were beautiful between them, they traveled together a good deal. They were checking off destinations listed in the book "1,000 Places To See Before You Die." (Maybe they once discussed going together to Mexico?)
2. In her "48 Hours" interview, I closely watched Jodi's body language. She was cool as a cucumber the ENTIRE interview -- except toward the end, when TA's Cancun trip was brought up. This was the ONLY topic where Jodi acted slightly agitated.
3. Jodi told "48 Hours" she'd known about the trip for about a year, but never brought it up to him... So she goes and kills him the very day before he's supposed to leave for Cancun? The timing of this speaks volumes.
So IMO, Cancun seemed more the straw that broke the camel's back. Maybe Travis reneged on a "promise" about that trip, and she went to give him one last chance to make good. When she finally "confronted him like an adult" about her deep longing to still go on that trip as discussed, he didn't relent.
God only knows what he told her about the trip, or about the fact that she still expect to go (like an unrealistic fool). But whatever it was, it was the wrong answer in Jodi's mind.