Just to clarify, I wasn't the OW in this situation.
A very close friend of mine (male) had a long term affair with a female work colleague whilst he was married with 2 young daughters. Similar senario to the one you describe OP, he told the OW that "She was the one", "My wife doesn't understand me", "We never have sex", blah, blah, blah...
I knew the intimate details of everything, as he'd confide in me and navel gaze when we were on long shifts working together in a very stressful job. I knew the OW in question, also someone I worked with.
Friend was going to leave his wife for the OW, usual script, and then the wife he "never had sex with" unexpectedly got pregnant. He was given an ultimatum by the OW, either choose her and leave, or finish it. The OW was gambling on him leaving his wife.
He stayed with his wife and finished with the OW. He told the OW that he couldn't do it as the time wasn't right and he wanted to wait until his kids were older/had done their GCSE's/pick a text book excuse.
He told me (his close friend) that the OW wasn't worth loosing his kids over, or worth loosing his nice house and set up with his wife, and actually he didn't really love the OW either, even though she was a "damn good shag".
Knowing my friend, he was flattered by OW attention and instead of having the morals and decency to either end it with his wife before the affair started, or say no to the OW, he decided to have his cake and eat it.
What I think of his actions, is neither here or there, as I stayed out of it and didn't get involved in his personal life - his actions and the consequences were up to him. I did however refuse to lie for him to his wife and refused to act as an alibi. AFAIK, his wife knew of/found out about the affair and chose to work on her marriage, rather than him ending it with OW and his wife not finding out.
My very long winded point is; OW was completely screwed up over something that she thought existed and didn't. It affected her job dramatically (did I mention, he was her boss?), she was left hanging, hoping he would leave his wife, and she got very, very hurt and bitter. Whilst she was with him, she couldn't behave like friends around him, couldn't let on they were "partners", and was basically a sordid little secret for him.
I know he got off on the excitement - I think to a certain extent, the OW did too.
Seeing the destruction caused by both my friend and the OW to others, and themselves, I would say, like others, Walk away. Find someone who is single, can commit to you and you're not their "dirty little secret". You won't be able to be friends, OW tried it with my friend because they had to work together - eventually they both had to move departments because it was so awkward - for everyone.
Get a grip and let it go.