My Friend Just Got Pregnant For My Boyfriend...what do I do?

A few months after my boyfriend proposed to me, there were rumours 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 wicked 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 some friends say I should forget about both of them and get on with my life. 

But how can I? I want my man back from my back-stabbing friend.