Hello Nick, glad you returned
Based on my experience i can say that long distance relationship have a strong tendency to go down the hill pretty fast if the parteners are both 17 -22 age ranged...it's not a general rule but it's an age in which feelings/emotonal moods are maintained more via the primary senses (tactil/touch and optical/visual) and less via communication/verbal bonding. At this age a long distance relationship is more exposed to day to day temptations, bursts of based on uncertainty gealosy and let's face it , even in her group of girlfriends the novelty and mistery of the "new far away guy" wears of pretty fast.
About the vacations fights, my opinnion is that they didn't came out of the blue, considering this is a LDR (long distance relationship) and it wouldn't have matter if you are 100 miles away or 10 times more -> linking her behaviour to the Distance is not a true fact if you ask me (she was fine with it untill now)
Then again i don't think the fight you had prior to your departure had anything to do with it also....i bet that was not your first gealousy based argue the two of you had, so this kind of experience is not something new to her either.
I give it a 70-80% chance she either had a flirt or seriously started seeing someone else...her calling you now is just her reaction to loosing you BY YOUR CHOICE/TERMS as opposed to HERS and her continuos cold/moody attitude is her way of showing it.
If it was me i would have probably gone to NeverHeardFrom'sville right after that "tired of the relationship" line but you have to realise Nick that what is happening right now is not a relationship but a dragging towards the end at a snail's pace. I doubt it will ever come back to the happy days you had, but you can give it a try and talk with her, making her sure that you are unhappy with the current situation and her current behaviour. If she's not open to discussion and plays the cold shoulder card again , let her be - you are in your 20's and there's lots of fish in the sea...ohh and save some tears for the future girls/women you are going to meet...dunno why but men the tendency to run out of stock for one woman alone