Hitchhiking with a guy that's not my boyfriend Watch
If it is the former, tell him that trust is the key. Also, if you go and nothing happens, you've proven worthy of his trust. If you go and something happens, he knows you're not worth it. If you don't go, then he is just going to worry about the next pretty boy that comes along. Better to know, eh?
About the hitching - your uni wouldn't encourage it if it was particularly dangerous.