your ex-s soon to be wife sounds likea douchbag

I learned that if i thought that he CHOSE her over our family, it made me feel horrible...like why would he chose a loser drug dealer over his beautiful family

made no sense

and
it made me keep revisiting that place

I started to think of it not so much as a choice (like she was better) but more of a sort of he realized he didn't deserve me sort of thing

I know you are really hellbent on the douchebag having a relationship with your kiddos and I get that
but
how does an 8 year old "know the pain he put you through?"
why do your kiddos know that?

they are not old enough to process that information

make sure they are not pacifying you by disliking her
(I am not saying she is worthy of them...I am saying that they shouldn't have to worry about liking her and hurting you)

they SHOULD be having a good time with her
they SHOULD be liking going to their house

it is their house too
they deserve to be loved by a million people
they deserve wonderful things

it seems like you are glad they don't like her and that they shouldn't like her

but their relationship with her is outside of your relationship with her