My shadowmere has died so i am wondering if i use script commands to revive him is it cheating. I tried waiting for 20 days in solitude but when i returned to his death point, which was in the crevice in alftand, he was not ther and i looked around and he was nowhere to be found.

It's a single player game. It's only going to feel like cheating if you see it that way. I don't see the big deal with it though, you're just bringing back a horse.

Go back to right outside of the Dark Brotherhood sanctuary where you first get him and if he's not there, then it's probably that the game glitched out or something. To fix a game problem, it's excusable.

It's not cheating, it's creative problem solving.

its just you in the game. its only cheating if you care

Shadowmere respawns 15-20 days at the location of death according to uesp. So if you're patient enough, you won't even need to use script commands to revive him.