Do you think he'll still be interested in me in the fall?

If he still hasn't IMd you or contacted you, he is probably not thinking about you in a "I gotta have more with her" sort of way. He probably occasionally thinks about you, but probably never when he is able to communicate. The "absence makes the heart grow fonder" line is a little overrated in my opinion, unless there was that special connection (shared by both) when last you met. If you want to keep plugging away at it, by all means do so, but you shouldn't deny yourself the chance to meet other guys while waiting for Autumn to come. He definitely will not (as of now), so basically what I am saying is to keep your options open and put him "on the back burner on simmer" and have fun this Summer. You can still IM or send a postcard or whatever every once in a while (like every 2 to 3 weeks is acceptable and won't make you seem like a stalker), just to let him know that he was in your thoughts for a moment. In the meantime, enjoy your Summer and keep a look out for other romances. If those don't come out/around, you always got the Fall to "fall back" on. Good luck.