Well I read through it all. I’m actually glad you took the time to explain the whole background to the story.

My take:

McKenzie is probably lying about Ian being ok with this and lying about having even talked to Ian. She’d told you she wasn’t even wanting to go to England anymore then after you get upset, all of a sudden Ian’s ok with her cheating and lying? I also wonder if she was lying about telling ism about Tristan in the first place.

You have outgrown McKenzie. What do you have in common with her today? How much do you really enjoy her company? Not much, from what it sounds like. This happens sometimes. It’s usually best to end the friendship gracefully with well wishes and in a positive note rather than ghosting or waiting until you get in an argument, but what’s done is done and now you can move forward. Next time a friendship starts to sour, be brave and end it gracefully sooner rather than later.

Try not to dwell, even though it’s hard as this was a long term friendship and very hurtful. Do things to keep yourself busy, and try to make a new friend, even an online friend to help you during this time.