"vivait avec moi"
This is the past tense, meaning the person is no longer living with you.
If you want to say "used to live with me" in the sense that it happened in the past but it's not happening now, you can use the past tense of the verb "habiter" which means "to live":
"habitait avec moi"
For example:
* "Il vivait avec moi quand j'étais enfant." (He lived with me when I was a child.)
* "Elle habitait avec moi avant de déménager." (She lived with me before she moved.)