I was the OW. Twice.
The first time, I had a two year relationship with a man when I was in my mid 20s and he was early 40s. I genuinely had no idea... it was 20 years ago so no mobiles, he spent 5 or 6 nights of the week with me, we'd been on holidays, he spent new year with my family, etc.. it wasn't until I got pregnant with our daughter that I found out what he was up to. He had been deceiving both his long suffering wife and me (i was his second affair). I was utterly, utterly devastated. Heartbroken.
A few years ago I was involved with a man I met through a dating website who told me he was separated .. he wasn't.. twigged after about 8 weeks (too longer as he was living elsewhere for work).
In both these occasions the men deliberately lied and since we have split up I have experienced all sorts of crap they have tried to pull over both of our eyes (myself and their wives). I moved away from the first man, extremely manipulative, abusive and unkind. The second man, had been all sweetness and light when I met him but when I discovered the truth I must admit I went a bit apeshit. He attempted to leave his wife for me, and when i said I didn't want him, he went back to her/their kids, but was continually contacting me. I was cruel, I know, but I told his wife what he was playing at as she found my number in his phone and contacted me. I had a horrible time, he was threatening and unkind because I would not play his game and lie for him, I ended up going to the police to get him warned to leave me alone :/
I know my experiences are not typical, but I do feel that if a man is going to have an affair, he will lie to himself and to you. Claim the new relationship is amazing etc as others have said to justify their behaviour.
I will be honest; I am still devastated at what my daughter's father did to me even though this was many years ago. One minute I was pregnant with a wonderful boyfriend, next I discovered it was all a lot of fakery. But you will recover lovely Phee and there will be new relationships for you. My daughter and I are incredibly close; I have brought her up alone but she is now a wonderful girl just off to university. I am ridiculously proud. She doesn't see her father these days, that is her choice as she sees what a weak and selfish man he is.
Your children are your priority and they will keep you going. I would recommend making new friends who are lone parents too, meet up with them and hang out, they will get you through the weekends when people are having 'family' time -- but remember many of those families are full of unhappy people just going through the motions
I've been following your threads and wish you all the best... you are doing so well so far, I can identify with what you have been through, and I am sure you will blossom