I was with an abusive ex, we broke up, I kicked him out and my best friend in the world consoled me. She was there literally while he was leaving and being vile. She saw the state I was in. She would babysit my under 1 DD and everything.
A couple of weeks later she's seeing someone but it's new and I don't pry too much. Until I find out a month into it from a stranger who happened to mention them (small town, people talk) that it was my ex who I'd just split from and they are now in a relationship 
I talked to her every week and she had my DD overnight once a week and never mentioned it.
They admitted it when confronted. He dumped her once the damage had been done a month or so later, he was only interested in taking her from me. His last words to me were "I'll ruin everything you love".
My problem is I loved/love her to pieces. We haven't spoken since but I grieve for what we had and miss her dearly I'm just hurt.
Part of me thinks he's very manipulative (I know that) and she believed she loved him. But the other part knows I would never do that to my friend and can't understand how she put him before me. And that a real friend just wouldn't do it.
Would you get back in touch? I write emails all the time then delete them. I sent one once but found myself too hurt to reply to her reply (which was very remorseful sincerely). I think about it all the time and it happened 3 years ago. I couldn't care less about him or what he's doing but I miss her so much