Hope ... I get that you are totally reeling here and all this seems to have gone pretty fast.
Juts read your entire thread ... its missing something, something pretty big. Where are you DBing?? Updates are great ... but so far all I have read is ranting about the house, the OM living there with your kids, her treating you as an outsider .... if you want to flip this ... you have to take the time you have been given to start making some changes because just sitting back griping about what she is doing is not going to make you an attractive choice.
Here is the blunt truth of where you are, your W has taken all that emotional stuff she held for you and basically transfered it to OM, all the good stuff, without much more thought of ... "oh this jacket looks much better on me" ... at this point she could care less aobut your feelings, she fired you as a H and hired OM to take that spot ...... FOR NOW
You need to work on you, she is going to do her thing and nothing you can do to control that .. you can control what you do. Be a better father when you do have the kids, GAL ... 180... PMA ... I trust you have the books ... READ THEM.
You need to find yourself and rebuild what has been torn down. You will have to start gaining some respect from your W if this is going to turn around ... as far as OM and the A .... yeah most likely not going to last, might even be a good thing he moved in as that will speed up the process, one has a hard time hiding what a douche they are when they have no where to hide. Might be weeks, months, years .... are you prepared to ride this out? If so ... you need to use this time to work on what you can ... YOURSELF.
