From a woman's standpoint or point of view, this just doesn't happen overnight. It is more than one reason why this happens and you just didn't see the warning signs before now.
Respect begets respect. If a husband wants to be respected, he must respect his wife too. There are many reasons why a woman starts to disrespect his husband, sometimes it is because she knows that you have an affair with someone else other than her. It may lose her respect to his husband just like any woman would do. Just ask forgiveness, accept your mistakes and prove to her that you are worthy of having her respect back. Never make the same mistake twice just because you are forgiven a lot of times. Show a little effort if you truly want to gain her love and respect back.