What's the best way to get back at my friend who slept with my ex and lied about it

I don't care but why lie about it? Bitch move on his part

Confront him about it. See what he says.

Have you considered op that it was none of your business and you should move on without fucking up your life over old pussy?

And? Maybe he didn't tell you cause you'd flip your shit like you're doing now. And once again. Shes not your girlfriend, she's can fuck whomever she wants. Your got a problem with it? That's literally all on you

Do either of them have kids/younger siblings?
You could really hurt one of them.

you are in the wrong
get over yourself

YOU
AINT
SHIT

Sleep with him

In all seriousness, it's your ex. Both of you should have moved on and have separate lives. What your friend and your ex does shouldn't even matter to you.

I knew this guy since elementary. I felt like we were on the level were we could be completely transparent with one another. If he had admitted it to me I would have said how did my dick taste? Have a laugh and move on. I don't care who anyone sleeps with. Liars are the ones I can't stand.

Its a dick move. You don't fuck your bro's ex unless you have his blessing

Also I have another friend who tried to sleep with her and she turned him down. The whore has some semblance of standards. I wouldn've fucked as many of her friends as possible to get back at her if she had dumped me.