A lot of what is in your OP is very similar to my situation. I think some of what I say may sound familiar to you too.
My WH and I would go months (yes plural) without having sex. I had no desire, didn't care if I ever had sex again. It did nothing for me. I never felt sexy, never thought about sex, never had an inkling of desire. Over time, I got resentful and angry at my H. There were times when I would have sex with my H and be pissed off about it. HOW could he not see that I was miserable? HOW could he enjoy himself at my expense? I felt like he didn't care. I felt like I didn't matter. We would be in the middle of intercourse and these were the thoughts going through my mind. I would stare at the ceiling tiles and just wait it out. I would tell him to hurry up and be done with it. I would tell him that I needed to FEEL close to him in order to enjoy sex. I told him that he wasn't giving me what I needed. I couldn't articulate what the "things" were that I needed in any kind of tangible way. I only knew that I wasn't getting them. None of MY needs were being met. I told him I wanted more intimacy. I wanted to feel close to him. I tried to explain that when he was sexully aroused, I wasn't even at the starting line yet. That I needed more to get in the mood. Again, without giving him anything concrete to try and do differently. It felt like he didn't care enough to give me what I needed. But really, he didn't know how. And part of the reason was because I couldn't explain it to him. We were at an impass. We pretty much ignored it. Did't work on it. Let it fester.
NOT a reason to have an A. But I would be lying if I didn't say it was a contributing factor in creating our broken M. I played a part in not giving my H what he needed for a loving and happy M. I didn't even make any attempts at it. My H would often tell me that the fact that I didn't enjoy sex made him feel less of a man. He began to question his attractiveness and thought it must be him. He thought his penis must be too small (it's not) His penis had nothing to do with it as far as I was concerned but it meant a great deal to him. He felt emasculated. It was a blow to his ego, again and again and again.
Being in an unhappy M left him vulnerable to an A. For him, the A was mostly about ego stroking and how she made him feel good about himself. Lots of other factors too, but this was one.
So what did I/am I doing about it?
First thing is that I communicate better with my H now. I had to learn in IC how to do that. I wasn't sharing enough with him for me to feel close to him. We talk a lot more now-and I have to take the risk and open up to him. I found that by doing so I feel closer to him-which is really what we both wanted.
I figured out why I had no desire. For me, a big part of it was a medication that I was on that KILLED my libido. I weaned myself off of the meds and began to FEEL desire again.
I also began to do things to make me feel better about me. (I had really let myself go!) I cut my hair, started to exercise, took some pride in my appearance. I'm never going to look like I did in my 20's but I could do a lot better than I had been. I had stopped taking care of me-so I started to again. That in turn made me feel desirable.
I decided to let go of the "he said, she said" impass we had going on. Something had to change, so I did. I made a point of being more in the moment when we were having sex. I didn't let myself think about what I WASN'T getting and thought about what I COULD GIVE to make him happy. And THAT made me feel good. It makes me feel sexy, and like a woman to be able to "please" my H sexually. And that is pretty damn normal!
I let go of many of my "hang-ups" that I had about sex. I was uptight and reserved. I am working out why I am like that (thanks mom!) and learning to let it go.
I got a vibrator.(really, first vibrator at 42!??!) Not a scary giant one (maybe one day-lol) but something unassuming and non-penis shaped. I learned about my body and found that I could enjoy myself physically. And I got used to the fact that those feelings are OK. I let go of the embarrassment that I used to feel.
I hope that helps in some way. I think you just need to try RELAX a little. Take small steps if you need to but you have to take action to work on this. You can't just read and talk about it. It is scary, and it feels like a big risk to open yourself up like that-but you have to do it at some point. If you aren't ready yet that's ok. Don't be pressured into it-that will only breed more resentment and anguish on your part. Talk to your H about how you are feeling and make sure he understands your point of view. Make sure you understand his too. Come up with some baby steps together that will address both of your concerns and allow you to gage progress. Maybe that "positive feedback" will make you feel more comfortable to opening up to more. *hugs*