A couple things:
Why did you assist feed him? There's no reason (IMO) to do this unless the snake is deathly thin and will not eat on its own so you need to intervene or the animal will die (if I remember from another thread by you -if it wasn't you I apologize!- the animal looked no where close to being this thin). This could have stressed the snake enough to make him not want to eat right now.
Never leave a live mouse in with a snake unless it's a pinky/fuzzy as even small adult mice can cause harm to your snake if left unattended. Always supervise live feedings.
It sounds like you're trying many things very often: leave the snake alone for a week in between offerings. Some snakes take longer to acclimate before they start eating readily: leave your guy alone unless you need to substrate clean. How often have you handled/handling him since you got him?
My T+ will only eat when leaving a f/t feeder in with her: she's only struck off tongs twice for me since owning her. Some are very shy and will eat if it's quite and dark, maybe yours will start to eat this way even if it didn't take the one mouse the single time you tried.