How do I let him down easy?

I used to love this Cancer, he rejected me. We remained friends, but now, 2 years later, he is trying to rekindle the lost opportunity. I just don't have those feelings for him anymore, he's trying so hard and it makes me so sad to be so distant and cold. When he first told me he had feelings for me I told him flat our it would never happen. He seemed to think that it was about forgiveness, I told him that I just didn't feel that anymore...

Is there any special way to tell him how I feel without hurting him? Or at least, what is the best way to talk to him about this?

Oh I feel you. Bad timing unfortunately. I would simply be honest with him stating the rejection caused you a lot of hurt and you felt you had no choice to move on which led you to a loss of feelings.

Be nice. Did he reject you back then because HE didn't feel the same as you? There's no reason to be a beech about it. You've already told him (nicely) it's not happening that should be it. Give it to him straight again and let him deal with his emotions as you did in the past when he wasn't feeling you... He'll be fine eventually.

He actually ostracized me from hanging out sometimes. made it really awkward and avoided confrontation altogether. Him ignoring me was an answer, a really immature one but I got the hint. I dont want to be the same way.
He hasnt talked about his feelings since I told him It wouldnt happen. Hes just been trying to make moves.. subtle but clear. As an Aries I would prefer a mode where I could just tell him how its going to be flat out, but him being all subtle robs me of that opportunity.

If he can't be friends with you then you can't be friends with him. You've been honest with him and that's the best policy here. I don't think you can let him down easy but you can unwittingly feed him with false hope by keeping in contact with him. It's hard. You want to be friends and not lose that. Maybe if you took a break now, he might move on with him life and then you can reunite as friends. For now, I'd keep my distance. Good luck!