How to cope with the frustration and embarrassment of retroactive "cheating" accusations post-breakup?
TL;DR: My ex-girlfriend (F22) and I (M22) were contentedly ENM before breaking up for unrelated reasons. Now that we are no longer on speaking terms, she has told a lot (A LOT) of people that I cheated on her, even though everything was within clearly established boundaries at the time.
Basically, the story is as above. My ex-girlfriend and I had a relationship a little longer than a year. We discussed ENM on the down-low for most of it, but during that time, each of us had exactly one independent encounter outside of the relationship. We weren't public about this at all because she was scared of people misunderstanding or not respecting what we had. Nevertheless, we discussed how we felt about it, established boundaries, and handled things as maturely as we were able. While my encounter fell pretty comfortably within the boundaries of what we talked about, hers did not.
My encounter was with a guy (she didn't know if she would be comfortable with me seeing a girl, and I didn't want to mess anything up between us). We talked about it before, and we talked about it after. She called an Uber for me and wished me luck. It was a one-night encounter, and I left afterwards without staying the night or anything. I never spoke to him again, and it didn't cause any struggle or tension in our relationship.
Her encounter was also with a guy, her coworker, while we were long-distance for a summer. That fling lasted around a month, which I wasn't necessarily opposed to, and I enjoyed hearing about her experiences, etc. Later in their fling, she called me crying and admitted that she had developed feelings for him, and that it involved gifts, letters, and a level of overall intimacy that was beyond what we had talked about (we had agreed upon strictly sexual encounters). She admitted that she felt like she had to choose between us two romantically, which was hurtful to me.
I don't feel that these encounters are even remotely comparable. While her and I were still together, I didn't tell any of my friends because I didn't want them to dislike her if we were going to continue with the relationship, and I didn't want to reveal that we were non-monogamous. After we broke up, I described what she did as "cheating", because, in the moment, that's what it felt like. This is where things get complicated.
Regardless, she launched what feels like an organized smear campaign against me in response. People with whom I used to be cordial now glare at me or refuse to acknowledge me. Girls whom I try to date get "hey girly" texts from my ex or her friends warning them about me as a cheater. There is apparently an app for exclusively women to gossip about men, where my "cheating with a man" was made public to a lot of people. Of course, the ENM context behind the encounter is either omitted completely. I also identify as 'straight' publicly, so the idea that I had a sexual encounter with a man is something that I was deeply uncomfortable with being public.
The whole situation has been really difficult and affected my self-esteem. I am paranoid that everyone I know thinks of me as a cheater, especially those who have never discussed the situation with me. I am terrified to begin a relationship because I fear that they will find out about my past from the wrong sources and never give me a chance to advocate for myself. I was an imperfect boyfriend in countless ways, just as she was an imperfect girlfriend, but I strongly believe that what I did was within established boundaries, not an act of "cheating", and that it is unfair and damaging to label it that way.
Has anyone else experienced this? What did you do? How did you cope with it personally? How did you explain it to future partners? Any advice is appreciated.