Me (22 F) and my ex (25 M) have been more or less sort of together for the last 5 years and are in a situationship/FWB for the time being (we work in the same office). I really want to stop doing it. I know what I am doing is not healthy, I know it's stopping me from finding a potential Partner, I know it's unethical since he has a long distance girlfriend who has no idea about this (he basically cheated on me with her, and then got together with her), I know it's Pathetic, I know it's by no means justifiable, but no matter what I do I just cannot get over him. I have posted on reddit a few times before and the comments actually give me a push and for 2-3 days there is a shift in my mindset which makes me so happy that I am finally getting over it but after those 2-3 days I am back to square one constantly checking my phone for his messages, saying I am down for whenever he asks me out, worrying about him, caring for him, having lunch with him etc. I just want to get to that point where I am like fuck it I don't care anymore about him but I just can't. I don't want to waste my time anymore but just can't seem to get over him.

Any tips/suggestions/advice would be highly appreciated.

TL;DR - No matter what I do, I just can't seem to get over my ex/FWB of 5 years.