You could look at it like he's taking someone else's inventory and that is upsetting, inturn that is causing you to take 'his' inventory... Upsetting you even more.
You could first seek to understand him, and then be understood. Then let it go, and continue to work on yourself first and foremost, and let him be with himself.
That is what I strive to do when other people **** me off, lol, easier said than done,
but it is what I try and do. The only person we have control over is ourselves, the only thing we can do with other people is try and understand where they are coming from.
JMO
I understand your frustrations though. :ghug3