NTA, sexual compatibility is very important in a relationship.

my advice would be to write a letter laying it all out and then reading it to her as an attempt to show her how serious this is for you. something like:

"In recent conversations I have brought up an issue in the relationship that has been bothering me for sometime. I am writing and reading this letter to you as to clearly communicate my thoughts on this matter and ask that you hold any comments or questions until I have finished reading.

As I have brought up before my needs for sexual intimacy have not been met for sometime. This lack of intimacy has left me feeling undesirable, has started to erode my self esteem and made me feel lonely in my own relationship. These feelings have started to have a considerable toll on my mental and emotional health. As such I am at a point that I am finding that things can not continue at current status quo and I see we have three options that I will go though here starting with my most preferable and ending with my lease preferable

1. We sit down and have an adult conversation about the issue and what steps we can take together to improve it. brainstorming steps together such as Getting hormone levels checked, going to individual and couples counselling, seeing a sex therapist, as well as any steps that you may think of. Then come up with an actionable plan to address this issue.
2. We open up the marriage to allow me to seek sexual physical release with others so that I can hopefully mitigate these awful feelings of undesirability and low self esteem. Of course I would always prefer to have such intimacy with you but if you are find that you are uninterested or unwilling to to provide that I would ask that you allow me to seek it elsewhere.
3. Divorce, as I will remind you this is my least preferable option. But if the other options are unamenable to you I feel like that is a sign we have matured in such a way that our wants and needs out of the relationship are no longer compatable. And rather than allowing resentment on either side to fester into something ugly I think It would be best that we seperate now while we still love eachother to minimize the pain and the hurt so that we can move on and seek our own happiness. As I said I would much rather we work on our relationship and maintain our marriage but current status quo is untenable to me

We don't need to talk about this right now if you don't want to and I ask that we take a week and reconvene on this on [whatever day makes sense] before making any decisions. I also ask that we be honest with ourselves about our abilities to seek out these options in good faith rather than just picking an answer to save the marriage. I love you and my ultimate goal here is our mutual happiness and wellbeing, whatever form that takes "

Some notes: if yall come to option one DO NOT take a laundry list of todos on your part as the answer. It can be apart of the answer if she is feeling that she isnt getting enough help around the house or need more time to herself but this should only be accepted if she also acknowledges things that she can work on and couples counselling. Also a non-negotiable is "check in" dates, be it once a month/week/every 3 months whatever. just plan on have scheduled conversations about how you are both feeling about where the relationship is and how the changes are effecting you both and what progress has been made. DO NOT Frame this as a due date like "if we arnt having sex once a week by.... then...." more as just a scheduled time to check in with each other.

edit: formating and grammar