Is OTHER wrong in the post ? POST : First reddit post so lil nervous, and fully prepared to be ridiculed for this story.

Background: me and this dude dated years ago. Stuff happened, we broke up on horrible terms. Fast forward a year and a half, I get out of an emotionally abusive relationship, and me and person (we'll call him Sean) have started talking again. One night on Skype, Sean tells me he still loves me, and doesnt know what to do, because he doesnt want to date again. I say okay, we become a weird.. friends with benefits. Sean is long distance, he lives roughly 1000+ miles away, and a few weeks pass and Sean enters a new relationship.

This is where my regret comes in. Due to being a huge dumbass, I agree to continue the FWB without Seans girlfriend knowing, becoming "The Other Woman". I honestly hate it, and I end up ending it pretty quickly, again on bad terms. Anytime he sees I am sad though, whether through social media or friends, he'll come into my DMs and tell me that he loves me, he misses me, he'll drive me out to his state, we can do "things" together ect ect. I end up falling back for it, continuing being the other woman when I'm sad, and ending it again when I come to my senses and hate myself for falling back into it again.

I recently got into my first stable relationship since Sean, with an amazing girl, we'll name her Jane. I went full disclosure with Jane, telling her everything Sean and I did, telling her my reasonings and she says I should tell his girlfriend, as they're still together and has no idea, while Sean is trying to add other women into his relationship.

Me and Sean havent communicated in roughly 6 months, and I havent been The Other Woman in almost a year. WIBTA if I sent his girlfriend everything? I already know IATA for helping him cheat in the first place, but knowing she doesnt know hurts me, because I know I would want to know, but I also am scared of being the person to break that happiness.