Maybe this is his way of protecting himself - he gets mad instead of hurt.
Maybe this is his way of processing hurt - he lashes out.
Some people don't handle what they perceive as rejection well, or handle disappointment well.
Likely, you won't ever know, and it seems like that's okay. He is showing you a part of himself that you need to pay attention to in case he ever contacts you again. Until this happened, it was all sunshine and rainbows, so you didn't see this side of him.
Now you have, and it's a huge red flag. He's showing you who he is. Believe it.
His plan to leave for another place when he is done with school has probably been with him since he came to school, or, at least, he was not shutting the door to getting work wherever it can be found once he graduates. (The job market being what it is, that is only pragmatic of him.)
You and he saw each other for about three months and had a good time, but feelings developing "quickly and strongly" and never arguing, didn't translate into specific long-term plans being made.
It also sounds like possibly once he figured out that you were beginning to cherish hopes for the long term, he felt he should tell you he intends to move away after school ends. Maybe he should have mentioned it sooner, but maybe he was enjoying things, too. I give him credit for not stringing you along (by implying he was going to stay in your town after graduation) for the whole 21 months.
Anyway, learning his plans to move shocked and hurt you. At this point, he probably felt bad that things were ending with you feeling hurt and dumped, so he asked to stay friendly. (This was probably to reassure himself that he hadn't hurt you). You turned this down, which (after the fun three months) probably felt to him like a slap in the face. Then you reached out only a few days, but he took this coolly.
The enjoyable three months didn't change his intention of leaving once he has his master's degree. Given that he didn't upend his career plans to stay with you at all costs -- accept it, he is leaving in 18 months. Don't waste time thinking that somehow if you only understood why he is behaving coolly, you can get back to the fun you were having in the past three months. It sounds like that ship has sailed unless you only want to have casual fun for the next year and a half and then say goodbye.
Ah, sorry to read this for you. It sounds like it has been painful. Love hurts is such a rotten thing to have be true.
Maybe he was worried that not only you had feelings but he did too and he doesn't want to get distracted from his ultimate plan. And the few days of your kind of taking a break cleared his head to realize it. In reality, you two weren't going to 'be just friends' before he left. You still had feelings. He either did or didn't. And just being friends with feelings like that is never a good situation.
I'm sorry this happened. Dating is a rough thing sometimes. And sometimes the circumstances just can't work out. I would not allow him to get lonely and try to reconnect with you either. Now it's your turn to be sensible knowing there is no future and trying to maintain a relationship with him under the guise of friendship will just lead to more hurt than you already have. Hang in there. hugs
I wonder, had you known that he was likely moving in a couple of years, whether you would have gotten involved? I think that him not telling you of his intensions from the beginning is wrong of him. Lying by ommission is still lying and i question his ethics. Even though you had fun, I think if it were me, and there was any more contact I would voice my opinion that I thought his choice not to be upfront in the beginning, shows poor judgement and lack of ethics on his part. I would tell him that he owed me an apology.
Sure hope you are doing okay. Hope to see you again soon around the forum.