Mate it's a very tough thing to overcome.
The fact you've broke up and a person you trusted has tried to take over.
The thought of you not being as good as your friend is shattering.
The thought of them two alone is shattering.
At the end of the day, theres nothing you can do. Trying to manipulate a decision only digs a bigger hole for you to get out of. The more you talk to her, the more frustrated you get at not being able to have her.
I'm talking from endless experience of shit relationships, where so many have gone wrong; and so many have ruined me for weeks.
You need to stop all contact; do not even acknowledge that she exists for a couple of months, you need to go out.. and find female attention and this way you wont become lonely or let everything get to you. The more feamle attention you get; the sooner it goes away. The sooner it goes away; the less time it takes next time you have a break up. This will then become minimal.
A way i love to get back at girlfriends or friends who have fucked me over is to show them i'm a better person without them. For example; after breaking up with someone recently for reasons unknown to man. I decided to hammer the gym and get a much better body than before. Then i would stop going clubbing for a few weeks and physically become bigger and leaner. Then when you look different, and healthier, and better off, they tend to want to know how.
Another way i look at it is this:
Theres 6 BILLION people on this planet, you have just come out of a relationship with someone locally to you. Someone round the corner if you will. There could be the perfect partner ANYWHERE on this planet and your moaning about a break up with someone who lives ten minutes away from you?
Just something i tend to say to myself when I decide whether or not to get upset
Hope this helps dude!
Pickup Truck