Please don't waste energy stressing about what the boyfriend will think (easier said than done huh?) I always get the impression women are more gossipy than men, be it to warn or put down or talk about each others love lives. Men usually strike me as more interested in making their own observations and decisions about a person, at least I've watched the ones I'm close to hear all sorts of things about romantic interests, and not care about anything other than the interaction they have with the person themselves.
It has been awhile now since you and Leo broke up, I don't remember ever getting the impression that you did, or thought you did, something wrong. Not sure what conclusions you came to when you went over this whole thread for introspection like you said you were going to do. I don't know if you think Leo & and/or his wife are saying things that ring true for you or just spouting BS. I was trying to look over the past to try to brush up on what happened, and I ran into some stuff you wrote in January about her going out with somebody you'd been talking to then having sex with them quickly (not 100% sure if this was the guy Leo broke up with you over).
I got the idea that you felt in a bit of a competition with her, and of course at that time were frustrated by your agreements to not be sexual with him, and then you found out she was not OK with you and Leo having sex. I wonder if you still feel in competition with her in some way, maybe just as a poly person. Maybe you are feeling upset you didn't do things differently/change agreements with Mono then and there, and it is coloring how you see things. I can tell that you are really uncomfortable hanging out in similar social circles but I'm not clear on how much of that is just your perception of the situation.
You posted a lot at that time before you broke up about how seeing Leo was stressful, I'm not clear if it was just the non sexual bf thing, you are clear that you two agreed you had different love languages, desires, and so on for a relationship. I just want to say I hate seeing that you are still being affected by it over 6 months later, when at the time it always seemed like you were trying to be clear and honest and loving. Maybe you should reread your posts in February about how you know you didn't do anything wrong?
Sigh anyway, I just don't like you still being tortured by this, maybe its a west coast female support thing? I know the whole issue is wrapped up in a confusing tangle with Leo and the woman Mono was talking with coming back, and new stuff with Brad and the horrible high school feeling of "that girl is talking shit about me and I don't know whats being said and I feel kinda paranoid every time I meet somebody new who might think badly of me". I wish I had a good suggestion, but I'd just say if you have a counselor, ask for some, or pick up your favorite book that reminds you that you're awesome.
Happiness will never come to those who fail to appreciate what they already have.