Had a FWB for over 2 years. Naturally RP (from family not ex), slim, highly feminine, submissive, gorgeous but didn't know it type. Easily the best chick I've been with by a long shot. Long story short I kept her on rotation (had a few lesser chicks going), didn't escalate it much with texts etc or asking how work was, let her do arranging dates when she had time off work, but when we were together it was very close and date-y and I found myself getting very emotionally attached to her. Anyway, because I used indifference game for the entire time, expecting her to validate herself to me over time, but she read it as total non-investment, so she naturally entertained new prospects and was getting fucked by another dude since summer. I sensed something had changed so I outright asked, when she told me and said to her that I'd actually come to love her and I couldn't go on knowing what was going on. Turns out she'd fallen for me me but didn't want to run me off so never pushed for more. She was practically begging me to start again with her but in my mind I can't see her the way I did before. The fact that I've been sharing this chick that I basically loved has caused a huge rupture in my psyche and my ego. I know she was never mine and never felt like mine but I'm ruminating on the fact that my setting a few boundaries here and there would have prevented all this. I'm plagued by a thousand what-ifs. And the oneitis is fucking brutal. My emotions are screaming that she was this amazing chick that would have been great as an LTR, that I missed out on this incredible experience that I never got to have with her. She was a real gem. But I can't go back now, not after my guy has been dropping it in raw every week as she bites his shoulder.

Ever had experience with this? Any advice on what to do, or how to let go? How do I rationalise this? I'm trying to not let this derail my whole shit.