Have you ever done it? Would you?
Now-DP and I have been friends since we were teenagers. I moved away for uni and lived with X, who became a very good friend. Now-DP visited me, and started dating X, and they were together for 3 years. Then they split up, X moved away and dated someone else for 2 years, and now-DP dated several other people too. Over this general timescale I had two boyfriends of 2.5 years each and there was no flirtation between me and now-DP. Now-DP and I remained friends with X but didn't see her much due to distance.
Then, I split from my ex and now-DP and I started dating. We kept it quiet for a month or so (as we share a social circle and rightly knew it would be major gossip) then came clean, and I called X to let her know before she heard from elsewhere. She has barely spoken to me since.
Now-DP and I have been together for 3 years now and are very happy, but I still feel sad about losing X as a friend and miss her. She wanted to stay friends with now-DP but not me, due to my "betrayal of womanhood," as she called it in an email.
AIBU?