OK I’m going to assume that this is the same guy who sent you the song in your first question. And the same guy in most your other questions.
My answer based on that, seams that he is interested in at least keeping the friends with benefits going. However I don’t believe that it’s just physical, because he’s had another relationship since your time together. I believe that he feels that the two of you flow together and he likes the physical part too.
You also have an interest in this relationship. So there seems to be an opportunity here, for the growth necessary, for a solid relationship to occur. I do not know why you don’t trust him. That is for you to evaluate. As far as what to do let it flow naturally and don’t switch gears too fast. If you’re going to be leaving to school again let that be upfront.
When you go back to school your leaving will provide proof of the summer’s relationship. If what you develop takes hold and becomes something more, it will become painfully obvious to both of you. You may just have the opportunity for one of those great meant to be relationships. Take it a little step at a time and don’t try to force it. If nothing else you will have a great summer of memories to add to those from the past.
And like delirium said in your next question “Babe, those ain’t subtle”
Don’t try to decode the man, you both want the same thing, “a great relationship for the duration”. And you both think you may have found it. I hope you’re right go for your dreams.