I was cheated on by my partner and my best friend. She was married, I was not but thought having my partner's child was the same committment and treated it as such (stupid and naive I know). Our children played together that's how they got together.
This was 24 years ago the kids were 3 at the time. When I found out I chucked him out and they moved in together and she was pregnant within weeks (We had been trying for another baby at the time).
I was devastated, they never, ever acknowledged what they had done to me or their children.
But I have gone on to live a very happy and fullfilled life, I have managed shared parenting and was able to have half the week where I was not tied to the house and children which I discovered I rather enjoyed.
I still destest them both and would not piss on either of them if they were on fire. I am not consumed with bitterness, I rarely think about them, but I will never forget or forgive. I still manage to live perfectly well and this idea of being consumed with bitterness is a load of bollocks. I can hate someone and still have a great life where, unless she oozes into somewhere where I feel safe and comfortable, (it has happened) it does not affect me. This idea of bitterness eating us up is nonense, hating them is perfectly natural, they destroyed trust and their smug "we did it for love" is no excuse, they did not even know each other but went crashing into a relationship and later, marriage and now have two very unhappy daughters who both have mental health problems because of the circumstances in which they were conceived and born. The two children who were thrust together into a "blended family" (liquidised more like), hated the girls who they saw as the product of their parents behaviour and the reason they were no longer able to live with both their natural parents.
She and he will always be the other woman/man to me and her ex husband. I call her my son's current wife (but not to my son obviously). But consumed with bitterness, nah, totally disinterested until a thread like this crops up.