I'm not going to give back my ex's stuff
Do you have a reason for not doing this?
Handing back his stuff is not a rule in my books.
You should return things that do not belong to you. It is stealing to keep them.
Those things are my things too right now. I might give them back eventually.
Well I hope you do! Would you like it if they kept your things? If a relationship is over you should cut the ties so you can both move on.