My close friend is pregnant for my fiance

 few months after my boyfriend proposed to me, there were rumors of him being sighted with my close friend at that time. He tried lying about it but my so- called friend admitted they were an item and she was pregnant. A few days later, my fiance called to tell me the engagement was off. I was devastated. I later discovered that he’d been seeing this ‘friend’ for months.
I feel humiliated and betrayed, and anger is the only thing that has kept me going. All I can think of is wreaking revenge on my ex-fiance and my so-called friend.

As things are now, I am embarrassed to see anyone and rarely go out. I’ve written a nasty letter to both of them to let them know how much pain they’ve put me  through, but all I really want is for them to feel my pain and for everyone to know they can’t be trusted. My parents and friends say I should let go and go on with my life, but wouldn’t  revenge release me to do that?