Wait why is he leaving? Can someone explain?

so basically cain wants to defeat satan and his army once and for all so he can safely live with joon without worrying abt satan’s army coming after them. he also hasn’t fully recovered from his injury and his power hasn’t come back to him yet so it’ll be hard for him to recover and protect joon at the same time. so he’s going back to hell to just do everything he plans to do basically and he doesn’t want joon to follow him and find himself in danger so he made the doctor tell joon that he’s not coming back for him. i hope that made sense haha (●'◡'●)ﾉ

Thanks! Made prefect sense, but i somehow didn’t get it form the dialogue :’