I'm female and that happened to me. I didn't get that we had to buy a new house because he wasn't happy.... with the marriage. I look back and see the signs but the truth is, I was blissfully in love and willingly took his excuses that he was distracted because of work.
The sucker punch goes either way, I just think women are better at planning for it quietly and dealing with a bad situation until time is right to leave. I have yet to meet a man who dealt with a bad situation quietly and didn't need to make everyone around him as miserable as he is.
I was aware of a problem, its just that I was assured repeatedly that the problem wasn't us or me but work related. I guess you could say the OW was work related....
It is devastating to go from, " I am so lucky and I love my H so much.... life is so good right now.... what could happen to mar this?" to " What do you mean you don't want to be married?"