I am wondering, isn’t texting a short-messages kind of communication (I don’t text), and do you have his email address which allows for longer messages?

You are right, though as we’re both quite young email isn’t really something we’d normally use for even longer messages. It would feel too formal.

If you were to send him a longer message (including in it a question or a few words…)

I’ll try it out here:

Hi [?],

Hope you’re OK. I had lots of fun on the course this summer. I know we talked about this a while ago, but there are a lot of things I feel I didn’t manage to clarify with you. First of all, I want to know how you felt about me then, and how you felt about me now. Second, I want to know if you’re really OK with us staying in contact as friends. And third…I’d really love to get to know you a bit better! You seem like a great guy.

Hope that helps…