Why is it so difficult to get him to stay in touch?

My boyfriend of almost 2 years has been in Europe since September for school. He's returning this weekend. The only way we've been able to communicate is online because calling is expensive.

He last talked to me 2 1/2 weeks ago, despite my attempts to message him and I know my messages have been read. He's never been the most communicative type, however I've spoken to him twice before about how his bad habit of falling out of contact hurts my feelings.

While I understand it is his last couple of weeks there, and he just finished finals, I don't understand what's so difficult about dropping me a message at LEAST once a week, which I've expressed to him in the past. Am I asking for too much? Is it wrong to be so angry at him right now? I'm not sure how to approach this situation, obviously my previous discussions haven't had an impact. His family has also experienced my frustration as he's had sporadic contact with them as well. Any advice or insight would be appreciated.
Why is it so difficult to get him to stay in touch?
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