6 months is still pretty fresh and you may still have flashbacks every once in awhile. So if I were you, I'd cut myself some slack.
You're doing great with NC. Continue on - block him wherever is possible. As far as telling his girlfriend, yeah, he lied his way out of it and they are still together. But from my personal perspective, I'd prefer to know if my man is a liar and cheater. She may not believe you and he may have told her you are stalker and liar and whatever, but the thing is that sooner or later she'll catch up on the truth.
She didn't win anything. He is not the prize. They guy you are with now, is. Appreciate what you got, after being tortured by the man who showed you no care or respect. Forgive yourself for still having some residual feelings - you were very invested in him, and got hurt badly. It may take awhile, it's a process, but for now, just protect yourself and your very fragile heart.
Good luck.