We all go there, thinking that the other person was somehow something we are not.
The truth is, they are, they are two things that we are not. But it is not what we think about, it is what we don't understand.
The OM or OW is available to do what they did, and is willing to do it, that is it, nothing more.
Your spouse was the same and all that happened was that two of those people ran into each other, both who fit that bill of qualifications, and you have an affair.
It may be hard to understand, nearly impossible to believe, but that is all there is to it.