First of all, we are so sorry for your pain. And no, this is not your fault. What your husband has been doing is wrong, but you did not cause him to sin. We are all responsible for our own actions.
Because of the deep emotional wound this sin causes, you will likely need spiritual and professional help (pastor, Christian counselor) overcoming your hurt. Similarly, your husband will need help overcoming his sin. If your husband is willing to get the help he needs, praise God. Encourage him to follow through. Though it may seem impossible at the moment, at some point, we pray by God’s grace you can forgive your husband and be part of the help he needs. Your support and loving accountability can play key roles is his eventual victory over this sin.
If your husband out of fear or denial is not ready to get help, pray for him. Show him this web site. Seek help for yourself and request the prayers of your pastor or Christian counselor for him.