First - I hope you told her that you had that affair way back when (either at the time or now). Affairs are usually signs of other problems in the marriage - here, it was lack of sex, and interesting/fun sex at that. The talk of the affair could open you both up and strengthen the relationship by allowing you both to fully recommit to each other. Then again, it could end the marriage - it's a risk - but it sounds like you haven't fully forgiven yourself... you won't be able to forgive until she knows about it and forgives you. That conversation could lead to the sex issue - she'd probably take the sex conversation seriously at that point.
Second, I applaud your response to your wife's statement about 'most couples.' The issue is what works for YOUR marriage, not what works for 'most couples.' You need more sex AND the sex needs to be more interesting. You might not want to hear this, but both of you are at fault for the poor sex. By not having sex, your wife may (because I'm not her, I do not affirmatively know what she thinks) be telling you that she needs more from you. As women get older, their sex drive decreases, same with men. However, a woman's sex drive appears to disappear completely. Fortunately, it does not.
A woman's brain operates differently than a man's. While a man can automatically focus on sex and get in the mood immediately (an overstatement, but not too unjust), a woman can not -- or I should say MOST women can not. While you are inside of her thinking about how hot she is / how good the sex is / how much you love her, she is thinking about chores she needs to do tomorrow, what the kids are going through, the finances, etc. A woman's brain alternates between these things all the time (the old phrase 'nagging wife' is actually founded in science! She's constantly thinking about everything that needs to be done and she will think about it until you get it done).
SO, you have to talk to her. You have to stress that she might not consider this to be a problem but YOU do. Sex, for men, is an expression of love - it's not just about pleasure. Most men can not communicate feelings; so, they communicate with sex. Women need the communication before the sex in order to get turned on (there are exceptions to every rule, but generally speaking that fact rings true.) An explicit conversation may not be helpful because she already dismissed this issue. So, start off in a non-traditional way: change your behavior.
Communication is not just words - it's everything: little gestures (buy her flowers, make dinner one night, pick the kids up, do the laundry, make a romantic dinner for two, etc.), physical contact (not the chest grope - though she may like that, I doubt she wants it to be an every hour thing - this is more about creating anticipation. More appropriate examples: kiss her goodbye when you leave for work, rub her lower back when you're standing next to her, give her a shoulder massage, gently play with her hair, etc.), and a lot of loving affirmation (tell her how much you love her and how much she means to you - it's probably best if you catch her off guard with a well written letter. If you notice she just casts it aside or doesn't bring it up, then there are more serious problems and you should definitely be in counseling.)
The little gestures show her that you care about her happiness and that you'd like to make her life less stressful (though it may not seem like it, 80% of household chores are down by the woman - most of them tiny little things without which your life would be hell.) So by telling her that you'll make dinner tonight and do the kids' homework while she sips a glass of wine and relaxes, she is actually hearing that you understand the stress of her life. Warning: you will still have to put up with her criticism and your gut reaction will be to read the critiques as an insult - do not do this. Not only does it obviously destroy the moment you've sought to create, but it also is not an appropriate reading of the situation. Her criticism is her expressing her feelings - she usually does these things and now that you're doing them, she may feel like a failure. Reassure her that you just want to help out and that you'd like your wife to have a night off every now and then.
The physical contact is crucial. Most intimate touching becomes muddled in relationships as you. You stop wanting to pinch her ass because, frankly, you feel that you've grabbed it enough. So, start off small - if you kiss every morning before you go to work, surprise her and pull her in for a longer, lingering kiss. Mix things up. Start LIGHTLY touching her as you walk by her- emphasis on lightly, gently, intimately, etc. Lightly touch/brush her arm or neck with your finger tips, or lightly drag your hand across the back of her head, back, ass, etc. This touching creates a more intimate connection between you both (she may start to return these little gestures, though do not be disappointed if she does not do so right away.) The message is clear: you're my wife, I love you and I'm the only one who can touch you this way.
The point is to create an atmosphere of want and anticipation without providing the big pay off: orgasm. Make everything about her. You're rubbing her back not so she'll sleep you with - you're rubbing her back because she's stressed after a long day. The intimacy will follow for both of you. After a while, these gestures should become more teasing and playful. At that point, step it up and add the explicitly sexual stuff. Start massaging her down there while she's standing in the kitchen reading the newspaper or doing the dishes (note: there should be no dishes to do - you should have done them for her!). Catch her off guard but don't make it a 'I'm horny let's play' kind of scene. Initiate with a gentle hug and kiss - tell her how much you love and appreciate her - then slowly build to the sex.
Remember, sometimes it's better to walk away after getting her so turned on that she can barely stand than it is to turn her on and bring her to orgasm. Sex in the laundry room can be exciting, but getting her half-way to heaven and playfully walking away will make her want you even more when the lights go off in the bedroom later that night. She might start to return the gestures and start surprising you at work or when you're reading on the couch, etc.
Lastly, (this response is really long but I do believe I can help you haha) the loving affirmations are crucial. You need to write her the long and detailed love letters. You also need to start leaving her notes - leave a post-it in her wallet that says 'You mean the world to me. I love you - your husband.' The point is to make these affirmations so random and randomly placed (though not randomly placed enough to not require thought) that she'll wonder why the hell she's receiving them (warning: if she reads cosmo or other trashy magazines, she might think you're doing these things to ease the guilty of a recent affair - you have to reassure her that you just want her to know how much she means to you.) As I'm sure you remember, the best feeling in the world is when you see your girl smile shyly after you've said or done something for her. You have to make her feel special again. Don't bring up the notes if she doesn't. She may not have found them yet or she might be confused by them - when you start changing your other behavior, she'll get the hint.
And dude, after you've started integrating all of that into your daily routine, before, during and after sex you still need to get her completely focused on you and the moment. Her multi-task brain will want to veer off when she gets bored - don't give her the opportunity to get bored. Make the evening about her - cook a romantic dinner after you put the kids to bed early while she relaxes elsewhere (if they're older, then tell them to shut themselves in their rooms for the night), then talk about her - What's going on in her life? What did she do that day? Is she fulfilled in her job? Is she fulfilled as a housewife? as a wife? as a mother? Is there something you should be supporting her in that you are not? Talk EVERYTHING about her. Let her steer the conversation. You don't matter here - it's sad but true. IF you successfully put the spark back in your marriage, and this method is the continued method of use (it might not be - after all, you have to find what works for you and her), and you feel like you're putting in too much and not getting enough back (guys need to feel loved beyond being our family's bank account and our wife's orgasm, ya know), then you need to start talking to her about your needs again. And, at that point, you really need to make her listen.
All of this is going to be hard - there are going to be times when you think she's being selfish and doesn't care about the effort you're making. You have to struggle through it all. You married her - you're stuck with her. Marriage is hard. If you thought it was going to be all sex and desserts and oceans of happiness, then you were fooling yourself... big time.
If nothing changes or if things get worse, then it's time to get a professional involved. I hope it all works out for you :)
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