Setting boundaries example: "I love you and I trust you, but I really don't want you rummaging through my stuff. If you want something, just ask."
Gaslighting example (?): "Stop stealing my stuff." "I didn't take your stuff." "Then why is my <whatever> missing?"
Perhaps not a good example on the gaslighting, as you weren't too specific. The main difference between the two should be clear: the first is proactive, the 2nd is reactive. The first takes courage to initiate, the 2nd is a reaction to the pain of feeling anger that one wants to avoid.