"But I don't want to reject a good thing if something really good could come of it. But I don't want to string him along making him hope for something that can't happen."

You sound completely undecided, which is to be expected in such a short time. He's really nice & you have a lot in common. If it doesn't work out, that wouldn't be stringing him along- it would be giving him a chance. Sounds like you should be giving yourself a chance, too.