You are in a tight spot--no pun intended.
The problem here is that you have had a poor sex life for decades. And the longer a pattern continues, the harder it is to break.
For the last ten years you have had no sex at all. Before that, you tolerated a poor sex life. Now you find yourself busting at the seams. Is this new? Were you always frustrated? If you were frustrated all those years, did you try to solve it and fail? Did you never try?
I am asking all these questions because the answers are vital to helping us understand the exact nature of the issue. Without talking more with you, it would be hard to know exactly why this pattern has continued for so long.
For example, did your wife like sex at one time and then turn off to it? Did she never like it from day one? You will need to remember back to the early days. If she liked it and turned off, then we can suspect that anger extinguished her drive. And, if you can recall when it stopped, and work through those issues, you may be able to turn back the hands of time.
If she never liked sex, from day one, and you tolerated this for all these years, it would be helpful to explore what part of you--again no pun intended-- needed to feel so frustrated. No pattern continues unless it is meeting the needs of the partners on some level. That level is oftentimes unconscious. So, if you can admit to having felt frustrated all these years, then it would be good to find out what part of you needed to tolerate such sexual frustration. Do you have guilt about sex? Do you feel that you deserve to punished? Do you need to resent your wife, and does her refusing sex give you an excuse? Only you can find this answer.
A pattern that is so entrenched has many layers and meets many needs conscious and unconscious needs. And, to resolve it you must understand and resolve all the layers.
So, if you really want to break through, you must find out why you tolerated the bread and water sex diet and why she did as well. Find out also what the lack of sex says about yourselves as individuals, and what the lack of sex communicates to each other. How does she want you to feel about her refusal of sex? Does she want you angry, hurt? How do you feel about her as a result of this refusal? Angry, bitter, hurt?
Then, examine what purpose those feelings serve you as individuals and as a couple. If you felt angry or neglected, ask yourself why you needed to feel that way all those years. If she felt in control and cut-off by refusing you, she needs to find out why she needed to feel that way all these years.
As you can see, the problem is complex. And, the only way you can get to the bottom of it, is to engage in an open and frank discussion.
The problem here is that I don't think your wife is motivated to change the pattern. She seems content in going without.
So, you will be the one to rock the boat, and get her to talk with you. Tell her how you feel, and ask her if she wants you to continue feeling so unhappy. If she knew you were considering having an affair, would this motivate her to resolve the issue? Sometimes, a crisis is needed to unhinge a pattern that has lasted so long.
If there is love and a desire to maintain the relationship, then both of you should be able to work this through and rise to the occasion. If you are stuck, contact me again in my private consulting section and we can do an e-mail consult.
Good luck.