Is he just letting me down gently? or is he really interested but also very sensible?

I would be inclined to believe that he is telling the truth in this situation, from all the facts that you have given. It sounds like he realized that he was falling for you, and started to get scared so he backed away. If he has been hurt before, then this is quite a natural reaction, and the best thing to do is to just give him some time, and follow his advice and work through fully getting over your last relationship as well. Let him call you, and don’t chase him, and that way you will find out whether he is genuinely interested. If it was just a line, then that will become apparent fairly soon, by whether or not he tries to keep in touch.