I think that you really should be honest with him, that is the best approach here. Since you respect him and he seems to be a nice guy, you don't want to hurt his feelings, and turn him into a jilted guy who roams around like a wounded bear.
Tell him exactly what you have told us, that you care about him, you find him attractive, but you just are not ready yet, because you have not dealt with or healed from, your last relationship.
If he is the reasonable, decent person you have described he will understand, and not push you to go all the way with him until you are ready.
However, having said that, be sure of what you want because you run the risk, that after speaking to him, he backs off to give you space and someone else snaps him up, are you prepared for that?
You don't have to get into a situation where you reject him.
Tell him about your feelings regarding relationships and tell him how much you value his friemdship. Underline the friendship part tactfully without making him feel that he's been rejected.
Ask him to try and understand how hurt you are from your previous relationship and see how it goes. If he is really interested in you and you in him it might just be a matter of time before you feel more towards him.
If it can't work on a friendship level you might have to risk loosing him. A lot depends on how he feels too.
You both sound like nice people and you obviously care about him so eventually it might work for you both.
Look, you are just out of one relationship and feeling distressed. In fact, we are not provided with many facts really to understand why you lost your relationship and from where this guy you like comes in. I do not know if this nice guy is the reason behind the break up or something else.
Anyway, if you want to be with this nice guy you like and you need time. Then in my opinion this is the time really to assess that if he is the right person to be with or not. I mean you should check your assessment about that guy. If he is able to understand your feelings then I would like to congratulate you and if he is not there when you need him most as a true friend then why worry.
True friends are rare you must treasure them and you should be worried when they are lost. Along with this give others a good friend as well veiled in your personality.
Say to him what you said "that I haven't healed from my last relationship but I do really like you, but I'm just not ready for a relationship yet!". Honesty is the best policy.