My ex moved away a year ago we never really ended our realationship now he's back and he still wants me but his older sister and I don't see eye to eye and she told him that she doesn't want us to be wit each other anymore help we don't know what to do should he disobey his sister

What the hell is that??
I only heard people listen to their parents, NEVER SISTER OR BROTHERS or something like that. That's ridiculous! He has to decide himself, or else, HE IS A JERK

If your feelings for each other are real. He's been away and came back to you. I don't know what the relationship is with his sister. But if the feelings are true, then he n eeds to listen to his heart and not his sister. Ahe could be jealous that he's in a relationship and she maybe not.