So me and my girlfriend (lets call her Kay) of almost 2 years broke up less than a week ago and she's blocked me because I'm talking to someone who I like. Me and Kay both admitted to losing feelings at least 3 months ago so we mutually ended things, and have been friendly with each other to save the 6 years of friendship we have. She's polyamorous, which always made me feel slightly uncomfortable but I never said anything because that's who she is (and she's sensitive so I didn't want to hurt her feelings).

Kay dated 2 or 3 different guys in the 2 years we were together, and liked a couple more as well, but I always brushed it off because I thought that if I told her I didn't like it, she would get pissy with me. When I told her I want to take a break, she told me it was okay and then immediately asked if it was because of the girl I'm talking to (who I wasn't even talking to in that way before we broke up). I said no, but we got into an argument today because she feels so hurt and betrayed that I've "moved on" immediately after breaking up. I feel I should also mention that she's already dating someone who she's been talking to for about 2 months (they got together on Friday and we broke up Saturday). Me and this girl aren't even together and have no intention of getting together yet.

AITA for not telling her about my feelings sooner and, quote, "fucked off with another girl I knew I was right about"?