Jq…. When someone asks how you are feeling at work, just tell them you are feeling fan-frickin-tastic and give them a big smile. If they persist in bringing up your personal situation, just tell them you are focusing on moving forward in your life and you’d prefer to talk about other things.
I might think about looking for another job as well but I get that it may not be possible. Firm boundaries and a consistent message to coworkers will help. Can you change your work hours or the time you take lunch to cut down on the chances of seeing her at lunch time? Any options to work from home at all?
Try to get your sleep regulated. It really helps to improve your mood and anxiety symptoms. (((HUGS)))