Ended 5 year old friendship, For a relationship.

I don't know how to handle this situation.

This is first time I'm blocking certain somebody to save a relationship understanding my partners call. I [19M] didn't knew that my girlfriend was bothered by one of my female friend for a very very long time.

That Female friend let's call her "X". So I have been knowing X from 2021, We have only talked online. We only used to rant, vent and generally discuss any "tea", Once in a month or 2-Months. We used to only vent out to each other only if we've problems in life like in families or with relationships whatever.

My girlfriend didn't like our interaction. One day X contacted me after a long long time and I was trying to desperately help her with that situation, From that day she was not very 'ok' with it. She was holding up to tell me that "This particular person ( X ) is bothering me" but yesterday she finally opened up. She was obviously expecting me to remove her from everywhere.

Now I and X have many mutuals and I really don't know how to deal with this situation. How do I confront to the mutuals that I have blocked her for this particular reason.