I object on three counts.

Minorly, the endowment effect seems to be about valuing things more if I own them versus if I don't own them. If my jealousy experience can be pigeonholed into something similar, it would be valuing things more if someone else owns them versus if nobody owns them.

But valuing something more would presumably change the magnitude of my feelings, and that isn't what's happening. Jealousy is a totally different feeling to the sadness I feel from rejection. It's not just a more intense version that I feel because suddenly I like this person more because she's with someone else.

And that formulation also doesn't explain why it's relevant that she had a chance to reject me.