I think my boyfriend is cheating on me?

My boyfriend and I have been dating six months and out of those six months he has been away for three because of work. When we first started dating we called each other all the time and texted each other. Now that he's been away for so long he's starting to seem distant, like he never calls me unless I ask him to and even then most of the time he doesn't and says he feel asleep before he could. And when I try to call him he never answers. I know he's busy with work and I try to call when he's off, but he's schedule changes sometimes. And I know he does get tired, but it only takes 5 seconds to send a texts. I've talked to 4 times in the last month and a half about how this is bothering me and then after 2 days he goes right back to being distant. I know long distance isn't easy, and it definitely doesn't make it easy that there is a huge age difference (he's 30, I'm 18). But i just don't know any more, like I don't want to lose but if he's not happy any more I wish he would just say so. And I'm not even sure he is cheating or not, but sometimes I feel like he is. And it just recently started to feel that way.
Yes he is
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No he is not
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I think my boyfriend is cheating on me?
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