Do you think the switch from saving the earth to leaving it had to do with her wanting to get away from him? Maybe even unconsciously?
Can't speak for anyone else, but that was definitely my take on it - especially with the beginning contrast of "A man loses a woman" vs "A woman discards a man". Imagine being her in the situation. Your boyfriend comes around and is sweet & the perfect gentleman for a couple of hours, before switching back to his boorish young self (possibly with no recollection of what he'd said previously) the very next time you talk to him. No wonder she wanted to be as far from him as possible!
Listening to this one while driving, I'm sure I missed details; but my interpretation of the vision where the earth is a wasteland is the timeline where he goes back enough times so that he 'succeeds'. He gets what he desires (her), but in doing so she never gets the time apart to research saving the world OR leaving it. Ultimately, a man's selfishness dooms everyone.
I'm a sucker for time-travel stories. This time around was no different.