Hey Chubby,
You are just beginning through the emotional process that is a break up. You are in denial at the moment. Not so much denying it happened, by denying yourself the right to mourn, denying that you had a good reason to do what you did. Breaking up can often hurt the breaker more than the breakee.
It's the disconnecting from the person you were with that is the hardest - you'll miss them. RIght now, you need to fill the gap that person has left with yourself as best as you can. Get into your hobbies, take up the gym, hiking, boxing - anything that can get your mind off what you are going through. Don't think about finding someone else to fill the gap, that is just opening yourself up to misery.
Close all doors on her. Watching from the sideline of social media is just going to tear you up more. Many women can use attention to help them through breakups, as they get far more attention than most guys, so seeing some guy even slightly flirting on instapram is gonna hurt.
And forget the friendship thing, it's holding you back from moving on as it is more a thinly veiled thread that keeps you connected, when the best thing right now is to be disconnected.
The vast majority of people in the world have gone through a breakup and have gotten over it, and you will too.