I’ve not been in this position, but here’s my two cents…
When feelings aren’t helping — try logic. (And vice versa!)

Here’s what I came up with…

I’m sure you want him to be as drawn to you as you are to him… and if he is busy fulfilling himself in non-relationship ways… I’m sure it would be easier for him to relate to you, connect with you, and appreciate you — if you were to keep having as many interesting (non-relationship) stories to tell as he does. This means continuing to do interesting things without him. You may want to explore the relationship further & be really eager to do that (that’s nice!) … but his going away has temporarily paused that part of it to some extent. Don’t waste away emotionally (only focusing on having a relationship with him) while he continues to experience other parts of life. I think it’s normal to be interested in what he’s doing — going to South America is interesting! — but give him things to be interested in about you, as well. Maybe this is a good time to find that balance of “interested in him” and “interesting yourself”, maybe…?
(Not that you are not interesting – LOL – but it seems like you are saying that you think you are focusing on him and your relationship with him more than you think is wise…? Or more than you are comfortable with? Or more than he can, given the circumstances?)

Don’t beat yourself up for wanting his attention, or for giving him yours… just maybe ask yourself “what am I doing/ being — for him to give his attention to?”
If you are mostly thinking of him about him & checking Facebook — what attention can he give you, personally?
The most he could say is: “That’s nice, you’re thinking about me… that’s sweet… Yeah, it was cool that I…” (shifting the conversion back to whatever you read on his Facebook…)
And that’s about it… Not much about you, or what you are up to.

Keep living so that he can stay as interested in you & what you are up to as you are in him.
Check his Facebook, that’s fine… but let him check your Facebook for your updates, too!
Keep having a full life yourself:
A) So that you don’t get lost in thinking of him and your relationship with each other, tempting as that is..
B) So that he’s not the only important thing in your life (aka: you still HAVE a life!) and
C) So that he can remain as interested in you as you are in him.

While he is away, don’t let him be the only one doing cool and memorable things with his life. If you do that, it will be all about him, what he’s doing, and his Facebook updates. He may be an important part of your life & you may want more (which is a good sign!) … but remember all that you are yourself & keep doing the non-relationship things that make you you, Don’t forget that a happy, healthy relationship is just one of many things you want…. even if it does top the list…. it’s still a list!

I do relate to that — “Oooh, you may be the one” feeling & I know how hard it is to not drool all over that — but now’s a good time to listen to that still, inner voice that knows when it’s threatening to make you forget what ELSE is important or is starting to make you lose your balance.
Not easy urges to talk off a ledge, I know — LOL!!!

But, I do think he’ll feel better about you if you are just as much your own person with things going on in your life as he is. You’ll be a healthier, happier person for yourself AND him… if you can find that balance.

Keep exploring the relationship with him, but keep giving him a world of things to explore about you, too!
He must be pretty great for you to feel this way about him… 🙂

Hope this helps, best of luck!