If a guy acts like he likes you during the school year, but then doesn’t try to get ahold of you all summer, what should you think?

So a guy at my school kept giving me a lot of attention at the end of the school year and other people in my class kept telling me he likes me. He flirted with me a lot, for a few weeks, and asked for my number. I gave it to him during exams (we had one on the same day) and we made plans to hang out soon (no specifics were mentioned). He seemed really interested but that was 2 months ago and he never contacted me. I know he didn’t lose my number because he put it in his phone after I gave it to him.
I thought he might have gotten a girlfriend but was told by a friend of mine that he’s definitely still single. Now I start school again in a few weeks and I think it’s going to be awkward. Oh, and I don’t have his number. I just figured I’d get it from him when he texted me.
Now I don’t know what to think. Why would someone do that?
If a guy acts like he likes you during the school year, but then doesn’t try to get ahold of you all summer, what should you think?
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