I'm doing a masters. My thesis supervisor made our relationship a bit more personal and friendly: added me on Facebook, invited me for couple of dinners and we used to hangout sometimes and talk on articles at bars. Now he's for some reason avoiding me, answers emails/messages after couple of days (he used to do it in less than a day tops) and very cold and short. A very big problem is that I'm taking a lot of credits with him this semester (individual research work) and not only I have this fear that he might give me bad grades (he can do that simply by calling my work low quality; there's no objective criteria for the kind of individual course that I'm taking), he might end up not writing me a reference letter for my PhD, which is bad because first, a lot of credits under the name of individual work will remain unexplained, and second, I suppose it's awful that the one that I have worked with a my supervisor doesn't write me a letter.
What should I do?
PS: He's not physically accessible until the end of summer, except that for a 2 days conference that we'll be meeting in a week.
UPDATE: I messaged him just like @aparente001 had advised me, but shorter (with the question that @cag51 suggested to ask face-to-face). He answered me in a minute a sat up a meeting time for that day's tomorrow (we were supposed to have a meeting before, which didn't happen). Then I realized that he has been only super busy and there's nothing else that plays any role (at least that's what he said). So, asking him worked even before a face-to-face talk. Thank you for your help!