Sorry you're in this tough situation Silk Chaos. How does the work thing play out? You don't actually do the same job but you are in the same building? Might it be worth it or even possible to re-locate your work to give yourself a decent chance of having space and distance from Z? When a person it trying to move on from someone, the hardest thing is when they have to keep seeing that person on a regular basis. Makes it harder for your brain to switch to a new gear.

I am glad that you are finding PC helpful. Other types of connections could be invaluable to you as you navigate this transition. Perhaps you could even try a volunteering opportunity. Even one day a month. It can really help with feelings of loneliness or disappointment.

With regard to Z, perhaps you could think about the situation as having tried something and learned that it didn't work for you and your life goals. You didn't actually do anything wrong. You are a person of substance seeking attachment in your life. No shame in that including when it doesn't work out as hoped. I wish you peace, Silk Chaos. (Great profile name)