<human>: Can you succinctly summarize the text in 1-3 sentences?

I'm 32 and wife is 31.  We're married for 11 years and have a 4 year old son.  We both work full time jobs.  Our relationship is emotionally strong, but ever since my son was born, her libido is non-existent.  We have sex, maybe 2-3 times a month, but there's no "fire" to it.  She basically just does it to appease me.  

I'm at the end of my rope.  I've talked with her before and she did speak to her OB about a year ago who pulled her off her birth control thinking that was the problem.  It wasn't.  

Each time I've talked to her about it she somehow turns it around to make me feel like some sex crazed maniac.  I don't think she's initiated sex at all in the past 4 years.  I just feel so depressed about feeling unwanted, undesired and flat out empty and now my feelings are turning into thoughts of perhaps she's cheating one me (Which i really don't think to be the case, but after such a length of time the mind wanders)

I've decided that tonight I will sit down with her after my son goes to bed and discuss this, but I don't want this to turn into another argument or have her turn it around onto me, making me feel like the a bad person.  

How can I approach this?  What can I say to her to make her understand how much this is hurting me and how badly it's effecting my self-esteem?
<bot>: Wife has no sex drive, I'm going nuts.  Going to confront her tonight, how do I not fuck this up?