how do you cope with living apart after spending all your time together for years?

Gf (29) and I (32) have been together for 3 years.
We started dating because we both needed someone, liked each other and it was convenient. It grew into living together constantly, being always together through the pandemic, including quarantines, always having each other to turn to and somehow making it work without too many fights. It included a cross-country camping road trip, living by ourselves in a state where we knew no-one, going back to camping for another summer and into the fall. So lots of one-on-one time alone. Overall everything is good, no major issues, she adores me and has hinted at getting married.

Fast forward to this past Jan and life circumstances beyond our control has put us living with our respective parents, 1500 miles apart. She started a teaching job that she seems to want to continue through the 22-23 school year.
I’m moving a further 1500 miles away for the summer for work (There is no real work for me in either her state or my home state). And I have no idea where I’m going in the fall. I’ve been trying to move to the western US for over a decade and it keeps failing.

I love her very much and miss her terribly. Over my life, I have always been alone and had been used to it. In the last three years, I got very used to having a constant companion and these few months of being apart has made me realize how much I miss it and how much I truly need it. And now, we’ve reached a point where there’s no end date. I honestly don’t know when I’ll see her again and it could be more than a year (neither of us have the money to fly or drive to visit)

How do you deal with such a situation?
And what happens in the odd chance you meet someone else, similar, but who is present and not 3000 miles away?

Tl;dr: Gf of 3 years and I are now living apart, not by our own choice, and I’m struggling with it.