Guy's Behavior

The guy I’ve been seeing for a while just ended things and I don’t understand why?

Ok so for the last few months I’ve been seeing this guy that I use to work with. He recently went on a big trip to Ireland and reached out to me the week before he left (this is when we first started talking). The whole time he was gone we were talking non stop! There wasn’t a day that went by that we weren’t talking. When he came back he told me that he was moving away in August but that he really liked me and was open to starting a long distance relationship with me. I was open to the situation as I also felt the same. For a couple months things were great! But he just left to go on a big trip with his best friend/roommates and we don’t know when we’re going to see each other again. Things were fine before he left but something chanced around the time he was leaving. I noticed it and asked him what was going on and he basically ended things with me over text out of nowhere.
The guy I’ve been seeing for a while just ended things and I don’t understand why?
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