Guy's Behavior

My boyfriend is giving me 1 word answers and isn't continuing the convo?

Is there something bothering him? We're doing long distance and whenever we text recently, he's giving me 1-3 word answers and texts. I feel like something's up but I'm not sure. I don't want to make any assumptions because assuming everything pisses me off. For example, I'll be all heeeeyyyyy and he'll reply with "Hi" & he tends to reply with "K" and whenever I say something like "How are you" he replies with "Fine" I'm not expecting anything specific, but even if we're in phone calls he doesn't talk much and he isn't really himself... If you know what I mean. Do you think there's someone else? Am I boring him? Did I do something wrong? Am I annoying? I'm just very confused and this has been happening over the course of the last 2-3 weeks. I try to show consideration by asking "How've you been" and "Is everything all right?" but I don't want to be annoying so I don't do it often. I'm honestly really confused. Please reply ASAP and if you need any clarification just ask and I'll clarify as much as possible. Also, we're in a pretty serious relationship and I haven't seen him in real life in over a year... He moved a couple thousand miles away with his family about 2 or 3 years ago. I'm just really confused and worried. answer ASAP please please pleaseee!
My boyfriend is giving me 1 word answers and isn't continuing the convo?
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