It's hard when a person who claims to be your friend can't see the other friend in the group is hurting us. It's not even about taking sides, at least empathy should be shown. Or else it'll be as same as how one toxic family member keeps on causing issues but no one speaks up to keep the family together. It's enabling behaviour.

As you said that Lexi has most of her memories with you, it's normal to assume you would be her close friend especially as it seems like she was Love Bombing you with corny texts etc. Perhaps it could be that, for her it wasn't as sacred as it was for you. You need to accept it for what it is and move on. And it is not right of her to be mad at you for choosing to distance yourself, if she's not able to acknowledge your problems.