Any advice on how to get someone out of your head?

First, welcome to Fluther,

I wish I could give you some gem of wisdom that will heal a broken heart. There is no quick fix that I know of though. Time heals all wounds. And the more you involve yourself in other things, with other people, the less this will pull at you. Definitely talk about it with your friend too, and explain how you feel conflicted. That should help them understand why you need to be somewhere else when your friend is with your ex’s best friend.

Perhaps some of my fellow Jellies will have additional ideas.

If I can just say… (excuse my language) but that is fucked up.
I went through the same thing. It sounds to me like you are in high school, because that is when I experienced this same situation. It hurts, it’s drama, and it makes you frustrated.
I am sorry you have to go through this. You will learn from it, but at the time it just sucks.

I would, personally, find new friends. That’s what I ended up having to do, and I made some better friends that I had way more fun with. No more drama!
If finding a new friend is unreasonable to you, then I would just hang out with your friend alone, and she can hang out with him alone. As for parties…. maybe go to them when you know he isn’t going. It’s hard when you aren’t invited, so I’m sorry about that. :/

ah, I’m probably not helping. But you’ll get through it, girl.

Start dating. The easiest way to get over someone is to date other people. Eventually you will either find someone you are more compatiable with and no longer feel the need to be in your ex’s company. Or at least it will open your eyes to other possiblilities. This will only work if your committed to making dating work.
If you start to compare, remember how you wouldn’t like it, if they did it to you.
If you make your dating list of qualities to rigid than you are only looking for excuses to not date.
And don’t consider dating, looking for a serious relationship. Just look to widen your pool of friends.
In time you may not forget them, but you will realize you don’t need x person to make you happy.
Part of the problem with letting go with most people is they feel an emptiness. So fill it up with a lot of other new friends.

Welcome to Fluther!!!
Ignore him, eat some chocolate, watch a scary freaking movie, when it scares you, you wont think of anything else other than am I gonna die tonight

Listen to the song Over You by Gary Pucket and The Union Gap on Youtube. this song will have special meaning for you.

The only thing that has ever worked for me was getting involved in something else….anything else and getting very busy with it.

Replace them with someone else.

Why are your friends not inviting you to their parties but inviting him? I’d get some new friends- new guys will come around on their own.

avoid them completely- destroy all pictures you have of them, take their number off your phone, remove them from all forms of social media. Forget them in no time.