she got NTRed from you? i am sorry to hear this :/
life has taught us: if you have an osananajimi, dont let her go too far away from you. and dont let your best friend/random annoying dude get close to her.
I don't ever remember being NTR'ed. And evening Shiki.
She wasn't exactly an Osananajimi, per se, just a girl that I knew for quite a while, in both Primary and Chinese school. Never had an interest in her so it's all good.