Most Helpful Guy
He's definitely interested, but it isn't clear yet what his interest is. He seems to have been right there with you last week, and took it up a notch with rubbing your back. To find out where he wants to go, put yourself forward a little. Go up to him when you see him instead of waiting for him to come to you. Look at him directly and openly. Smile. If you're up to it, flirt a little - maybe even a little more openly than you are normally comfortable with. Touch his forearm when you talk to him. And then wait to see his response. You will have reached out to him and showed you were open to his next move. But he needs to take that next step if he is interested. Let him do it. Be a little patient, but he should respond right away if he is really interested, and by the next day in any case.
If he does, respond playfully but openly. Have fun. And if he doesn't, you will not have put your friendship at risk. Stay friendly, and a little touchy-feely, and who knows - he might find his feelings grow more romantic. If not, you still have a fun friend, unless your feelings are just too strong to allow you go on that way. If they are, and you would rather risk the friendship than go on as just friends (or as special friends if he is interested enough), then tell him how you feel, and be honest about how you feel about going on as friends if he is not interested in you more romantically.