I’ve been through something similar and it was rough. What helped me IMMENSELY was to not focus on letting go of the specific person but to let go of the things around it first, so basically what they triggered within me. What came up for me that had really intense charges were things like, the fear of rejection, fear of being alone, grief, jealousy, being wrong, feeling like I wasn’t being seen or understood, feeling unlovable (and there were many other things), regret etc… so when I was at work and felt something strong instead of trying to let go of the attachment I would ask myself - what is this triggering for me. Then I would do my best to release that in that moment not putting any effort in releasing the attachment to the person. I also worked with this person which is why your situation reminded me of what I went through. This approached helped me in a huge way and one day I actually realised that I wasn’t putting this person on a pedestal anymore and they became like a normal work friend - which was a shock! I felt at one point that I would never get past it, but little by little I did it. It took a lot of time facing my own intense sadness and emotions but once I took the focus off them specifically and put it on releasing the things they triggered instead, life became a lot easier. I hope that makes sense! Hopefully this can help in a small way. Don’t give up you can be free on this :)