My best friend was in a relationship witha married man for years, I don't think she was a slapper at all.
She was in fact a young, naive and stuid 17year old girl that met a guy who didn't tell her he was married straight away.
She later found out he was, and had two children of his own and a stepdaughter, she was devastated, but by now she was hooked, many a time she ended it with him, he always told her that him and his wife were 'just together for the kids' and other sob stories, so much so that even she thought him staying with his wife was the right thing
A few years in the wife left him, taking her two eldest children abroad and leaving the son, compounding what my friend had been told about how the wife didn't treat said son properly hence he couldn't leave.
My bf spent 6 months playing happy families with the boy, she then got pg herself, and wife decided to come back to England, bf became the partner and wife the 'OW'.
Thankfully bf had a termination (which 4 years later she still isn't over) and left him, but this went on for 7 years!
Yes she knew it was wrong but the picture he painted was one of an evil wife, that was a bad mother and he daren't leave for the sake of the kids.
He is still with his wife, and turns up at my friends work/house every few months, yet claims she is obsessed.
What I mean by this is we only ever have one side of the story, we don't know what horrors HE is telling OW, although it isn't excusable maybe we'd understand more if we did know?
Also, another spin, my dad left my mum for my babysitter when he got her pg. My mum then left Scotland so I didn't see my Da for years, him and the OW got married, and after having my first brother (who has SN, which is apparently what kicked dad into leaving my mum)they went on to have another, she too was with my Dad until he died of cancer a few years ago and is adorable. The reason my dad didnt leave my mum was her illness, he caught her trying to kill me and herself, so was petrified, only leaving when he thought she had got better.