I am in engaged relationship a heathy happy one, I am not very well experience in sexual experiences in life

[NikkeJoe22]

I really want to experience a threesome with Fiancé and one of her Best Friends but I know it will never happen, I have brought it up before because they have experience one back in High school, she has two best friends who I would love to do it with if she were to asked who do I want to do it with, but I know better then to bring it up, if it were to ever be brought up in the situation I’d be okay with switching partners, I am only thinking like this because I am a horny freak and I only see her friends in a sexual attraction because they see me as an ugly guy, I’ll never cheat on her with them at all regardless if I ever experience a threesome or not, but what should I do to erase this from my conscience and brain, one of her best friends knows that I want one the other doesn’t know.

[Vacuity]

The means to really erase something from ones mind makes it totally not worth it. You'll have to bear it until it doesn't comes to your mind anymore.
However I can give you a few tricks to make it quicker.
1 - find a good reason for not wanting to think about this. The best one you can. And then repeat it to yourself each time you do.
2 - picture a bottomless room. Put everything you don't want to see in your head in this bottomless room. Picture them falling endlessly without anything to grab. Let them fall into oblivion and only to keep falling.
3 - redirect your thought. If you think of someone else than your fiance, find what is appealing for you and try to find it in her.

But at the end those are techniques to alter your own mind. You need to ask yourself of you really want to go that far.
4 - protect your mind as a holy private space. Use it as you wish, and never let someone else dictate you what should be inside. Don't alter yourself when you can do otherwise.

No one will read your mind. If you want to fantasize just do it. And behave if you have to.

I hope it was not too much arrogant of me to say this. But I wish I helped you. Good luck.

[NikkeJoe22]

@vacuity thank you for your words Of wisdom, I will continue to redirect my thoughts else where.