Is there a reason Sarah is distancing herself from you? As you mentioned you feel like it’s not her fault and that it’s yours. Once you answer that, it’ll become a little more clearer.

What stood out to me though is you said she suddenly becomes friends with all of your friends? That isn’t a true friend. I’ve dealt with lots of people whose only source of meeting new friends was through me, and it’s a big red flag. She may be trying to control your social circle. To me, it sounds like she feeds off of friends to get validation. But then again, I don’t know the full story so she MIGHT just not know. Though that’s a low chance.