I’m so sorry for your pain. Your husband seriously broke your trust. You didn’t state how long this has been going on. If it is a recent and brief lapse, it’s one thing. He could have been reacting to your more recent marriage and the responsibilities that come with it. But if it’s been going on the entire time you’ve been together, it’s another thing all together. In that case, he has never been fully committed to you.
If it’s a recent lapse, please consider seeing a couples counselor to help you both understand why this happened and what the two of you need to do to put your relationship back on track. He needs to show you a sincere effort to win your trust. On your end: The marriage will only survive if you can return that effort with forgiveness and a willingness to move on.
Most marriages go through rough patches. If this was a panic reaction on his part, it seems to me that 8 years together is worth the effort to get through this. With work and compassion, the two of you can come out of this with a relationship that is even stronger than it was before. But if he’s a chronic cheater, you may need to rethink whether you want a marriage on those terms.
I wish you well.