I don't think Cancun had anything to do with it either. I think it all came to a head around May 28 when Jodi staged the gun theft -- I think she had been considering it even before that when she made her plans to visit Ryan Burns. What happened on May 28 to drive Jodi to making a final commitment to murder Travis? Well, that was the day that Lisa got in touch with Travis again after not talking to him for a couple of months. Likely Jodi knew exactly who Travis was talking to and when -- no doubt she had access to his online phone records. May 28 -- three days before she rented the car and started her trip.
It was also around this same time that Travis found out Jodi was breaking into his Facebook account, and he told her to stay out of his life for good. How did he find out she hacked his Facebook? One possibility -- when she found out Travis had been talking to Lisa again on May 28, she logged on his Facebook and read his messages to find out what he and Lisa had been talking about, and then called Travis and confronted him about whatever she found. Just like she did with Bobby, and just like she had done with Travis when she had snooped on his text messages in the past.
I think Travis made it clear once and for all that it was over and there was no going back. Realizing she was never going to get Travis back, Jodi decided to kill him -- and at that point, I don't think there was a thing Travis could have said or done to change the outcome of what happened.