Its pobably just sex with you she has lost interest in. She may well still fantasise and masturbate. But.... Without the dating excitement, without the spontaneous sex you once had, without the chemistry you both felt, she just doesnt have the mood for it any more. Common as hell in most marriages.
Communication is all we have, and if you and she cannot communicate your way out of this, then you may well become another divorce statistic.
Talk, talk, and do as much as you can to reignite what you both felt in the early days. I wish you luck. It is Not easy.