i'm Jim. I had a relationship dissolve recently for a fundamental difference in viewpoint on the poly dynamic. The circumstances are not the same, and certainly i don't intend to hijack your thread. The feelings are pretty close though.
It's terribly painful to part ways with someone you still like a lot. I find myself thinking things like "but if you could just chaaaaaange," to quote my friend BoringGuy
The reality is, that isn't ever going to happen. The two of you have different expectations and goals, and they aren't aligning. That's ok, but it is painful. My condolences. It sucks. It especially sucks when you are in a situation where you get to see that former love frequently. There's evidence of that about 100 feet away from me at this very moment.
GalaGirl is absolutely right. Hang in there. It will get easier.
Best of luck