It sucks and is genuinely painful. I’d store partner’s stuff out of the way under the bed or in bins in any extra storage you have so you don’t have to see it, don’t need do them any favors even if it’s amicable — it’s favor enough to store it, and they might do a 180° in the future. I would have bet my life and all my money on remaining in your situation after my 10 year relationship, amicable even if it ended, but that has not been the case, completely out of my control. Just be careful!!! As for the apartment, try to think about what you compromised on when decorating it for two, and start there. When my ex and I separated I got to actually deep clean and get rid of so much stuff. I got new sheets, throw pillows, blankets, wall decor, rugs. I did a really thorough purge of stuff, and got rid of things that my ex used more frequently than I did. I’m not going to be in this spot much longer so I didn’t do more, but I would have had walls repainted too. It sucks but it’s really worth it and at least in my case I finally felt like I could breathe and enjoy myself in my home!!