ClingingToHope,
my x recently had a baby with her new H who was also the OM. and the whole situation threw me for a loop. lots of crap going through my head, very much similar to your own.

i think thats natural, just deal with it and dont dwell.

one excellent piece of advice that i was given is that this new child is my daughters sister.

and regardless of what i feel about it, my daughter is excited, and loves her, and is her big sister. To my daughter its the same as if it was her full sister, instead of her half sister (as i, in my shallowness, see it).

so its my job as her father to be excited for her, and not show her my own shortcomings and weaknesses and spitefulness. because if i do, then i will only hurt her feelings and alienate her and drive her away from me.

and its not easy, but it is necessary. forget your feelings for your xW or the new baby's father, focus only about your daughter and her relationship to the baby.

"In a ham and eggs breakfast, the hen is involved, but the pig is committed".