one sided? friendship advice

hi everyone, first time using this subreddit and i need friendship advice! we're on winter break from school right now, and my (F18) best friend (M18) is visiting family for a month-he's 14 hours ahead of me. he hasn't answered my texts in 4, almost 5 days. we saw each other before we left and affirmed the fact we are best friends. he hugged me and said he would miss me. we've talked a couple times when he's away, though obviously it's tough with the time difference, and we've been making plans for hanging out when he returns. i texted him on new year's eve at 10 AM my time to wish him happy new year in his time zone, and we talked for 30 minutes. he stopped replying, but came back after 10 minutes really apologizing that he was talking to a family member (whenever he stops replying or is late to reply he apologizes). i was okay with it as i myself was busy by that point, and texted him so. that same day, at midnight my time on new years, our friend group was hanging out (without him, of course) and i sent him a picture, then about 20 minutes later a pic of something i saw driving home. he hasn't replied to my text messages. this isn't the first time something like this has happened-over the summer, we were in different countries and he didn't reply for 10 days, which honestly hurt. we've grown closer since then and he's always sorry when he goes missing. he has no social media except spotify and goodreads and i haven't seen activity on the latter in days, but he was active on spotify 12 hours ago suggesting he was using his mac/phone and thus was capable of texting. maybe it's too nosy of me, but i guess i am a little hurt. he is the best person i've ever met, but a chronic procrastinator. i don't believe it is malicious, what he's doing, and maybe he hasn't seen the messages, but it happens during every single school break. he said he'd do better. keeping in mind that he is visiting family and a busy guy, but also that we are best friends and he keeps leaving me on delivered, is it one sided? or am i the problem, for worrying too much about it? any and all advice, commentary, etc. is greatly appreciated! :-)