demon!dean is like a magnifying glass.
he’s basically amplifying things that dean has felt and thought over the course of his life.
of course dean felt resentful towards sam and john. he loves them, duh, but that doesn’t change the fact that his life has been totally shitty and the demon part of him resonates with that.
he turns it up to a higher frequency.
but these are all things that dean has felt. it’s just that he can never bring himself to actually say this shit to people because he doesn’t want to hurt them.
he holds on to hot coals, only burning himself, not realizing that letting go is actually the first step to healing and moving forward with his life.