"ever" means "at any time". "always" means "all the time" .
Ever is the contrary of never, when you put "ever" in a negative sentence it means never, the same doesn´t happen with always:
I don´t ever agree with him= I never agree with him
I don´t always agree with him= sometimes I agree and sometimes not
In some cases "ever" can mean always, but in imperative or emphatic phrases and with some preposition like "as ever" or "forever".