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as someone who has lived abroad and done the quitting grad school at the last minute thing, i can tell you that all three of you are in a moment of transition in your lives.
i couldn't tell when i was in that moment that i was there, but twelve, fifteen years later, it sure is clear as crystal what was going on with me ... and with my drama-filled relationships.
you're about to leave your home state for a graduate program that will lead you straight into a career abroad. your ex-ex just came back from an extended waver, caused by immaturity and burning man (was that redundant?), which resulted in him recommitting to his original plan. now he's about to go back to grad school to execute said plan, which will also take him straight into a career abroad. your recent-ex is about to finish grad school, but has no further plans and is freaking out.
you're all standing in front of a huge life transition. it's not unreasonable to say that the decisions you make now will determine the course of the rest of your lives. all three of you. whether you HAVE a plan or purpose (as you and the ex-ex do) or whether you DON'T (as the recent-ex doesn't), you still feel like you're standing in front of a precipice.
i don't have any advice as to which boyfriend you should take up with. i WOULD advise you to cut them both loose and move on, but you might not be able to see this until you've actually moved and started grad school. in a few months, this dilemma will seem very small and far away. so do what you do, but remain open to cutting them both loose in a few months when you realize that you are moving away from them both, geographically and emotionally, and you need to give yourself room and space to do that.
the path you're embarking on -- one of international service -- is famously destructive to relationships. it's not just a matter of long distance relationships; you'll also be traveling a lot and meeting tons of new and fascinating people. the relationships that last are the ones where you can take your partner with you, or where your partner serves as an anchor and port for you. either way, until you're in place (which will be years from now) you won't know how to find the right person for you.
so try to recognize this as soon as possible, and let these guys go. you're not going to be any good to them, and they won't be any good to you.