It didn't work out for me...but it did for my DM.
She didn't know my stepfather was married as he didn't wear a wedding ring. They dated for a few months.
When she found out (I believe he told her) she ended the relationship. His then wife called her and actually asked if she'd think about taking him back.
Apparently he had told his wife what had happened, they were both very unhappy and his wife was pleased to have a 'reason' to leave him that would also mean he would feel guilty and therefore be very generous financially.
So she called my DM and basically said "I'm done with him, we're unhappy and I don't want him so will you consider taking him back because he's done nothing but mope about". 
Anyway...long story short. DM did take him back eventually after that call. Stepfather and wife divorced - he has now been married to DM for about 25 years.
DM and the now ex-wife have been friends since. We even all had Christmas together once (including the ex-wife's new partner) and when I was a child I went on holiday with my step-brother and the ex-wife twice and would sometimes stay over at their house in the summer holidays.
I would caution though that this is not the usual story and very much 'the exception that proves the rule' IMO.
I was also an OW several years ago. Mine was more the cliche ending and definitely didn't work out. His wife never knew - it was extremely emotionally messy for me including an abortion. 0/10. Would not recommend.