Sorry you have such shitty people in your life. Get your kid away from these assholes and hope treachery is not an inherited trait.

So you're not calling him your EX-fiancé why?

Forget them both, you and your child deserve better

Its clearly not meant to be. Three years is a long time to wait to pick a date. It must have been mutual. Best of luck moving forward OP

Your not alone. Just replace best friend with coked out stripper. And we are even.

Ex fiancé and ex best friend ?

I've dealt with something similar! my ex husband slept with one of my best friends twice in the week after we got married! we already had two kids together, I tried to stay and make it work and we had our third child (I know stupid idea but I dont regret having her) we didnt even get through another year and again he had started seeing someone else, so finally I told him he could do what ever he wanted because I was emotionally exhausted chasing after him. our divorce was official a little over a year later on xmas day! I'm happy to say I'm with an amazing person now who would never pull any of that shit on me and my kids! seriously, dont waste your time on that person anymore because you deserve so much better and your little one deserves to see mom/dad happy and healthy!