Why Kendall and Hailey are friends if Justine cheated with Kendall?

Isn't it kinda weird to be best friends with someone who have slept with your husband before? and who accepted to cheat even tho she knew he's in rltp , so is Hailey wrong for trusting Kendall?

Why Kendall and Hailey are friends if Justine cheated with Kendall?
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