If your s/o's ex moved across the street...
Would you move? Literally asking for a friend. Her boyfriend's ex girlfriend moved into the apartment building across from them in Manhattan. They both have dogs, so it's likely they'll see each other, since dog-walking times (morning and evening) are pretty standard.
Then there's the inevitable subway run-ins, bodega run-ins, etc etc.
The split was amicable. The ex gf is really cool and normal and nice. Which I think my friend finds threatening. They only broke up because the "timing wasn't right."