GF and I of a couple months have to break-up soon because of a trip. Any advice on how to mentally prepare for this?

My GF and I (same age: 19) have been together for the past couple months, however, I have to leave for a two-month long trip in July which would break us up. We both knew this day would come when we started going out, but recently I'm really hurting inside whenever I think about it. I lay in my bed and try to come to grips with the impending situation, but I'm always left feeling cold, gutted, and depressed. Whenever we talk about it, she tries to keep it lighthearted and comical, and I love her for trying to make light of the situation, but no matter what I feel terrible about it. On that day I feel like I'm just going to burst out crying as I board the plane.

She and I mean a lot to each other because the previous relationships we've been in were pretty shallow and more physically oriented. So not much love to be had there...

Do you guys have any advice on how I can mentally cope with the pain and sadness?

EDIT: Before y'all comment on why we can't just get back together after I come back, it is because she will be switching universities in the fall semester, so I won't be seeing her for a LONG time.