My partner and I were monogamous when we got together and for the first few months of our relationship, she was still sexting and flirting with her ex/now friend. They've known eachother upwards of a decade now. The friend didn't know we were monogamous or the level of our relationship during that time. When I found out and confronted my partner about it, she cut said person out completely with hardly any discussion with them about it.

Fast forward 4 years and said person came back into her life and we are now poly. They've kept a very positive and casual friendship since then. That was about a year ago. The friend has matured a lot and has shown a lot of growth from what my partner has told me. My partner has been very honest and communicative about their friendship now. When they initially reconnected a year ago, she told the friend about what happened and they were really apologetic and said they wanted to get to know me. I have told my partner many times that I still have a lot of uncomfortable feelings about this person, but she doesn't understand why, given the mistakes were made on her part and not the friend's.

She told me today said friend would like to talk to me the next time they video chat about my hobbies and such. I want to extend kindness and try to get to know them. We've been together 5 years and I've never spoken to them before.

There's just this part of me that is still uncomfortable and wants to hate this person despite them not having known and becoming a better person.

Edit: formatting