Can you leave another state without a guardian's consent if they don't have custody of you and the person you are going to see does have custody of you?

No. A legal guardian is appointed by the court to oversee the welfare of a minor until said minor reaches the legal age of majority or the court rescinds the guardian order or the guardian askss to be reieased from the obligation. A legally appointed guardian's custodial powers supercede that of the biological parents. Furthermore, the guardian would need permission from the issuing court to allow the minor to leave the residence for any extended period of time especially if the minor is leaving the state of residency.