I could be completely wrong on this, but, I think in his mind he needed an escape. Not just a geographical escape but, also, from regrets. At his age, he may feel trapped in a life without purpose and a waning time of opportunity. At some point in life, several us wonder "what might have been". This is especially true when you compare your everyday life with what is posted on social media. The reality is that life is not meant for a few great moments, it is about everyday moments. I think Tad got caught up in comparing his real life to the fantasy life he envisioned.
He saw an opportunity to not only escape but to do so as a hero for another person. In his mind, he is rescuing the pretty damsel in distress. He can reason why he is the hero for giving up his life in order to rescue her. He can justify his actions to himself by believing he is the strong and courageous hero he was always meant to be. Her following him and trusting him and giving herself to him only reaffirms the rightness of his actions.
I know this all sounds like a fairy tale and that is exactly the escape both Tad and Elizabeth and trying to capture. In reality it is basic emotional needs of men and women. Emotions are what drive so many of our decisions, especially irrational ones. Our mind then tries to create a world that justifies the decision. In this case, that world is a fantasy of the hero and the girl living in a tropical paradise forever.
This scenario is the primary basis for my theory that they are on the run, rather than hiding out, to that tropical paradise. For Tad, that very well could be a place and lifestyle he was exposed to on a mission trip in Central America. That place has the tropical weather, access to beaches, simple lifestyle, low cost of living, and far away from the past realities of life. At the same time, it is a place with less risk of being sought. It has the long term possibilities they see in their fantasy future.
From a drive time perspective, they could be there now.
How do they get caught? They may be found by an inquisitive vacationer or mission team member. They may seek medical help and recognized. Elizabeth may realize that this is just another case of entrapment for her and seek help. Tad may have a spiritual moment and turn himself in. These are all the positives and I hope it is the way this ends.
The above is my opinion only.
