Well, it depends on what YOU think.
I don't really believe that it might hurt a little explanation as long as you tell him exactly what you need (ending communication for good).

I had a similar situation with an old friend and i felt much relieved once i explained what the hell happened between us.

So i suggest you telling him what happened and also that you also no longer wish to contact him.

Also, once done that, try to cut the communication yourself.
Is what i suggest you. Reading more future replies would be a better idea.