I appreciate that you love your wife so much. Maybe she is disappointed with you about something but she doesn't know how to tell you. Maybe she wants to avoid quarrels or simply she doesn't want to handle her disappointment with you.
Think about something that she dislikes and it seems that the problem is solved but actually she had once received negative feedback from you and now she doesn't want to deal with that problem anymore.
For example, any relationship problem between your mother and her and you insist that she is not broadminded enough. Or, actually she is so tired looking after the kids and expect you to help out but you always have reasons not to help.
A woman is like that, if she doesn't feel safe or fond of that man she won't have interest to go to bed with that man. Maybe she really expects something from you but you often give her negative feedbacks and she just shuts up and for the sake of the kids she just stays in the house daring not to expect anymore.
If she really does not feel loving you, there must be something. I think because you have done something and that gradually she does not feel that you are "lovely" anymore. Ask her gently, but don't threat her that you think you two have no future etc.
I also appreciate that up to now you do not have affairs with other women. If one day you really can't stand the relationship with your wife, end the relationship with your wife first before you start another. Of course this should be the last step and hope it won't happen. Don't mess up one problem with another!