Probably by the time I write and post this, someone else will have said the same thing - so I apologize for repeating...
Anyhow, I think it was the May 26th text messages the sealed TA's fate. I think that's the correct day of the messages that ALV just loved to reference when Travis went ballistic with JA and told her she was evil and the worst thing that ever happened to him - and basically she was out of his life forever. After that I don't think it would have made any difference with JA even if TA ended up going to Cancun by himself. She knew she was out for good and nothing was going to change his mind. OK, maybe she went to TA's home in June with the slim hope that she could change his mind but if not, then he was going to die - so Cancun really had little to do with the outcome.
And BTW - am I the only one who doesn't think it was abuse (or even inappropriate communication as Dr. D put it) when TA called her all those names? I just cannot imagine a world in which all of us must think through, and mentally edit, each and every word we speak to another person especially in the heat of anger. Travis was angry - very, very angry - and from what Ive seen of Jodi so far, those "abusive" words seem to fit her to a T. I believe the saying goes - call a spade a spade.