Someone who sulks every time you see other people is shrinking your world to fit theirs.

Sulking is a quiet way of charging you for having a life. Nobody says do not see your other friends, and the cost of seeing them goes up each time, until you stop because it is easier. That is not jealousy as a feeling, it is jealousy running your calendar. A world that keeps getting smaller to keep one person comfortable is worth noticing early.

Go to the thing anyway this week, and say plainly that you are going. Watch what happens afterwards. Then say the honest sentence: I would rather you told me you were annoyed than went quiet on me.