What a disappointment for you both. Yes – both. You lack the sexual connection you so want with the woman you love. She finds that sex is not what she thought it would be. You are frustrated. She feels like she is always disappointing you. This could erode your marriage. Actually it already is.
Cheating is not the answer if you want to save the marriage. Having a relationship that works in every other way is not something to throw away easily.
My suggestion is that you take a very big step back. Instead of pushing sex, invite some very tender talk. Instead of focusing on your needs, ask your wife just what it is that makes her so unable to be sexually close. Did something happen to her at some time that left her unable to enjoy sex? Did she shut her sexuality so decisively off in order to stay a virgin until marriage that she can’t switch it back on? Has she been afraid she might hurt your feelings if she told you that there is something in your approach that overwhelms her? Stay as compassionate and loving as you know how. Explore her feelings without judgment. This isn’t a debate. It’s a loving discovery of what she has experienced and what she needs.
If there is something about sex that upsets her so, let her know that you want to help her through it. Suggest that the two of you might benefit from working with a couples therapist to help you learn how to communicate better when a topic is scary or difficult. If she really, truly is clear that there is no underlying reason for her lack of libido, suggest that she might want to have a complete physical checkup including a visit to an endocrinologist. Sometimes it’s in the hormones, not in the head.
I am concerned that the topic of sex has become so difficult for the two of you that you aren’t intimate in other important ways as well. Talking through this issue with love and understanding may help.
I wish you well.