First, be absolutely sure you want to do this.

Don't be petty about it.

Be absolutely clear that it's over.

Alert everyone in the entire universe.

Go make a crapload of tackles so everyone forgets you're the worst.

It's no secret that made up relationships are hard. When they're good, it's unbelievable...but when they're bad, it can drive you to the verge of insanity. Not to worry, I'm here to help.
Once you break it off, there's no turning back. Sure, you dreamed she cheated on you, but that was YEARS ago. Is it worth spoiling the memories of the state fair you didn't go to? Or the Snapchat she didn't send you?
Make sure to steer the conversation towards behavioral issues. Explain how sometimes she can be a pig.... and other times she can be a sexy nurse.
Tell her that your decision is final. She's not allowed to text, email, speak to your subconscious, tweet you, or send messages on Facebook....it's OVER. If all else fails, make up a disease for her.
There's nothing more embarrassing than one of your buds being all "Hey man...where's your (bunny fingers) girlfriend?" and then you have to be all "sigh, we split up" and then he's all "LOLOLOLOL". That's why it's SUPER important to tell ESPN that she died. Clean breaks, bro...
Nothing says "I'm not a horrible person" like being good at sports. USA! USA! USA!