Sorry in advance for the rant but I'm seriously pissed off.
I was with my emotionally abusive, serial cheating STBXH for 13 years before one final affair tipped me over the edge and I left. The OW in question took great delight in telling me that she was sleeping with my H and tried to play a pathetic game before realising I wasn't biting and doing the whole 'I'm telling you as a favour because you're too good for him' act 
. I stuck her on loud speaker and listened as my H and her had it out calling each other all manner of nasty names. I did some googling and found out she had a bit of a shady past with drug and alcohol addictions and a violent criminal record. A few months later she tried to tell me she'd made it all up and was just in a 'bad place'. I'd already moved out of the marital home by this point.
Fast forward 18 months and I've moved on. H struggled with me meeting someone else but I did what I thought was the right thing and told him about new bf before any introductions to the children were made. He tried to control the pace of that but I did it at a time I felt was right for my children.
So over the last few months my DC have been mentioning 'daddy's new GF' and all the things they have done with her and her children. It turns out it is the OW. I asked H if he was seeing her and he denied it. Then photos of them clearly in a romantic pose, showed up on facebook so again I asked him. He says that photo was a drunken one time thing but that they are just friends and not in a relationship. Putting aside the fact that she's a known drug addict with serious MH issues and instrumental in the breakdown of my marriage, I couldn't care less that he's moved on. Frankly they deserve each other.
BUT, to this day he still denies having an affair with her but has told her she did HIM a favour by lying to me?! I'm so cross that he's still lying about what went on but also acting like it was a good thing. I wasn't perfect in our relationship but I was damned close, putting up with far more than most women would. I'm also angry that he refused to admit to infidelity so then divorced me. I didn't want to drag it out so just agreed.
I'm just having a moment where I'm begrudging how utterly infair it all is and the fact that he's still a complete arse who is incapable of telling the truth 
.