Ugh, I remember that "replaced" feeling so well.
ExH and I split up in 2009. He got a new gf very quickly and suddenly SHE was the one going to his parents for lunch, seeing his friends, etc etc. I literally felt like he'd lifted me out of his life and just dropped in a new version.
The good news is.. These feelings fade VERY QUICKLY. Like, in a few weeks. I know it currently feels like you are going to be sad forever but I PROMISE YOU it disappears really soon.
Remind yourself that yes, she's experiencing all the fun/good stuff with him, but she's getting all the crap too. And you no longer do. Remember every irritating habit of his, every annoying turn of phrase, every mannerism -- SHE bears the brunt of all that now. Not you.
You are free to create a whole new life now. Start! Start now! Don't ever say anything to her, it'll make her laugh at you. Just float away like a swan. Even if you're dying inside, float.
And before you know it, you'll have forgotten that you ever felt this way. I honestly had, till I read this thread. All those bad feelings and emotions have VANISHED COMPLETELY. They will for you too, sooner than you can imagine.