Do they? I guess that's really the deeper level of the question. Because a whole lot of WW's come here and say "I thought we were in love". Which doesn't make a lot of sense, but, that is what is often said. Now, if they know "it's only for the sex" or the "guy is only there for the sex" then, yes, it does make sense.
I said this more lightly in my first response...
I am a successful, smart, intuitive woman. I read people very well. The narrative in my situation changed rapidly. But, it changed only in my own mind.
So, at first, the AP was pretty up front that he just wanted to have fun, didn't want to change his situation, etc. I got it, it didn't matter, and I was thinking along the same lines. At this point, I am not thinking I am actually going to have sex with him, I just keep talking to him because he was fun to flirt with. He was good at it. (Yeah, we all know why that is...and even at the beginning I knew why it was). But as the talking continued it was probably 70% non-sexual. There were things in common, finishing each others thoughts or thinking the same thing at the same time...I look back and know that the mirroring starts very early.
So I will echo the other female posters that say it's just wherever your brain is. So, the escalation of feelings kept happening through all the other talking/flirting/endorphins running rampant. And, soon you are ignoring anything logical, or "what might be right in front of your face" and you start projecting a lot of things that aren't there.
At this point the AP in my situation either caught feelings too, or more likely mirrored what I was doing to stay in step. I don't know really, and it doesn't make a bit of difference to me now. But, whichever it was it made what ever I was projecting seem more valid. To the point that when the opportunity to be alone arose again, then we moved to physical. You already are telling yourself a bunch of shit that already made everything else okay and you are now in the thick of a big fat lie...to yourself. (And, I am not minimizing the lie to the spouse is worse, it's just hard I think for BS's to understand how logic is thrown out the window.) You lie and brainwash yourself so you can keep getting the feelings. You feel alive, vibrant, euphoric. But, it's not the person that you are having the A with that makes you feel this way - you are actually making yourself feel this way with all the fantasy, projection, etc.
This is why by the end of it we sound like loons and connecting the dots with logic is difficult.
I think many men have affairs for validation as well. They may think it's about the sex, but I can tell you in hindsight I can clearly see that's the biggest thing it was for the AP in my situation.
I will also echo some of the other posters - the females are mostly all saying similar things here. I don't have any reason to lie about this, my H does not come to this site. I have nothing to prove to any one on here. I have many experiences in my youth that Hardroadout describes with faking my way through really shitty sex, and with people I was maybe only remotely attracted to at best. Why did I do it? For validation, attention, some company? The A really was no different. And, the sex was not the main attraction to me. I didn't sit around thinking "Oh I can't wait to do that". I was anxious for a first kiss, or this or that, but I was certainly more interested in being romantically swept up...so I saw romance where I wanted to see it (at every turn). I maximized any evidence of it and minimized any non-evidence of it. Our minds do that with a lot of things actually, we often focus on things we want to more fully than things we don't want to.
At any rate, I don't see myself as a victim in this. I was not a fool that a predator took advantage of. Whatever happened was because I refused to focus on any of the things I should have - firstly and most importantly not doing any of it in the first place. Secondly, ignoring reality of being used and taking in only emotional gratification. And I can go on. I did all of it to myself, so it really doesn't matter what motivations the AP might have had. It really doesn't matter whether he was using me for sex. What matters is I ignored all that and re-wrote the entire story and fell for everything hook line and sinker.
Another poster on this site said something I think was true - maybe it was Jorge - something to the effect of he could see a woman who had been married a long time being more naïve, or who had put on a few pounds and maybe took it off and was getting attention for the first time in a very long while. He is right, those things were powerful in my situation, and part of it. But, it also takes away the power of all the other things the person has going for them that should have directed them better from cheating. As I said, I am not a dummy, in the end I chose every single thing. I was not a victim of circumstances, or of a predator - I was a victim of my own lies to myself. My own delusions that was feeding the whole thing. I have gotten off point now but I think in the end the take-a-way is the reason the physical happened, and the reason that the man's motivations were ignored, and the reason that I did things I really could have done without (wasn't seeking) is because I decided them. There were skewed motivations behind all of it, but I kept choosing that path of escape at any cost.