current spiral

this rumination/OCD spiral began just over a month ago. i went out w some past colleagues from my old job, one of which constantly flirts with girls. im aware hes flirty but i have never shut it down when he flirts with me; because im much younger than he is and genuinely feel a power imbalance due to this, he had a higher role in my old job and i lack the strength to shut that behaviour down. this was my biggest mistake, because as the night went on and the drinks were flowing, my guard was down and he was very flirty. again i didnt shut it down and i just sort of crave attention as im an insecure person and thrive off any sort of attention. but once i realised what i was feeding into i was absolutely disgusted in myself, just genuinely disappointed because i have a boyfriend of 2.5 years, who i have never ever wanted to intentionally hurt. after i realised the situation was getting out of hand, i stepped away and felt so sick and filthy. this whole situation was not something i wanted and i was overall just really upset. the following morning i was suffering from very intense hangxiety and fell into a total rabbit hole of reassurance seeking, googling, using chat gpt, anything to try and make myself feel better. i even messaged the guy and set my boundaries that the flirting needed to stop, and even chose to seperate myself from him. but even then, i could not stop replaying every single little interaction ive ever had with this him. for example when he would stare at me when i first started working at my old job, then the work christmas party where he flirted with every girl and even touched some innapropriately. then the time i caught up and had a big drinking night with the same group only a few months prior to this incident when he admitted he found me attractive and i just didn’t understand why. but i told him yes, hes attractive but i have a boyfriend and im clearly not interested. my mind would ruminate on every single little detail, and try to gain 1000% certainty. every single scenario just upset me more and more and i could not stop ruminating, confessing things to my partner, reassurance seeking, etc. now hes appeared in my mind every single day, sometimes all day, and im just genuinely distraught. i feel like a fraud in my relationship, and a failure. ive told my boyfriend everything, and he knows of my ocd. yes, he was disappointed, but i know in my heart my boyfriend is the one i want and this other guy genuinely means nothing to me. but still, because he’s become a root trigger of ocd, everything i do somehow feeds into the thought of him. whether it’s a song, a word i hear someone say, literally anything my brain can attach or associate with him, it will. it’s draining me because i know how i really feel but it’s just the anxiety and distress i feel constantly that eats me up. i go to therapy now, but struggle to understand how on earth ERP will help me here. im also prescribed sertraline (zoloft) but have been on this medication for 8 years and i fear i am almost becoming immune to the effects? im not too sure. thank you for reading this.