Distaff competition never ceases to amaze. Once possessing, always possessive.

psst they're still fucking

It sounds like your partner's ex may be holding onto good memories associated with their past relationship. It's a tough situation, but be aware this situation is not unusual. Many have faced it and yes, it sucks!

Have you had an open and honest conversation with your partner about how you're feeling? I think a good talk is the next step to resolve how you are feeling. Ask your partner to get their jacket back!

I feel like communication may solve many of the issues you are facing here! Good luck!