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To my knowledge, Magneto has been an 'X-Man' before, but not for a long period of time. And for a lot of the stories, he is the X-men's villain. I think what the OP means by 'X-men' is the Beasts, Cyclops, Jean Grays of the team.
Im not caught up on any of the current ongoing X-Men series, so I do not know where he currently stands in those books. But in his solo ongoing, he definitely not an X-Man.