Some posts here to the OP sound simply spiteful.
On the one hand, it's generally agreed on MN and in RL that it's best to live apart after a split before getting together with another person.
Yet here, this man is accused of using that 'space' to edge his bets. Or other posters play Mystic Meg and know he will go back to his wife.
The assumptions are staggering TBH and are pure conjecture. Maybe the type of people who post these things should ask themselves why they want to do this? Are they trying to help the OP- or just play some kind of sick sport via a web forum?
My opinion FWIW is that this entire thread has grown out of all proportion. In RL I've known every scenario there is in relationships: marriages breaking up without anyone involved, marriages breaking up because one or both parties had met someone else, marriages that are 'open' and where people continue lengthy affairs.
I'm nearer 60 than 50. I come from a generation when 'morals' were very different and much of what is par for the course now was unacceptable.
My parents didn't believe in sex before marriage, were 'ashamed' that I lived with my DH for a few weeks before we married ( it was then called living in 'sin') , have a very dim impression of women who have children outside of marriage which to them shows a lack of commitment, but even they would be more kindly and tolerant towards this OP.
One- and just one- of many examples is that I had a close school friend whose father upped and left her mum for OW when they ( the adults) were in their late 50s/60s. It was sad, but everyone acknowledged that he nor the mum had not been happy for years, so it was for the best and wished them all luck. There was none of the hysteria which is on this thread.
I don't think affairs are good, but for this OP the 'affair' is over- she and the man are now living out of their marital homes. It may work out, it may not. They have their reasons for wanting to keep it low profile for a while. Whether it's more hurtful to be left for someone else than just be 'left' is debatable; everyone is different in that respect.
Going back to the Ops' original post, she asked for support . I think there must be around 10% of these posts giving that. The rest are vitriolic and quite honestly simply reinforces some people's opinions of how MN is full of vipers.