Is it normal that i hate my ex being nice to me

I very occasionally run into my ex with the partner she left me for, formerly my friend and not hers, and they always relate to me as if we're all still good friends. In fact the breakup was very nasty on their part and this has never been discussed, let alone apologised for.

These meetings are always unexpected and they give me kisses and hugs I don't want from them. I managed to avoid physical contact yesterday but still felt trapped into chatting with them in the street.

The ex said she'd been trying to find me for ages, I said "Well I haven't been hiding, I'm in the white pages book and on the net. I sent you an email ages ago and you didn't reply," and she said "Oh my computer broke down," Yeah, like you can't access yr emails from another computer?

I don't understand why I didn't say that at the time and only thought it, or why I didn't ask her about what was in the email, which asked about important stuff of my daughter's they took in the breakup. More importantly, when she left me she totally abandoned my daughter, to whom she'd been like a mother for many years.

Why am I nice to people who don't deserve it just because now they're being nice to me?

She asked for & I gave my phone number and I want to prepare myself to be a lot more honest if/when she calls me, because this nicey-nicey game makes me feel really sick in the gut.

(We're all women, by the way, just in case hetero assumptions confuse some readers.)