My dad and mom have remained together for 20 years after their incident and they seem happy today.
My father cheated on my mother with a friend of both of them. It took both counseling and a few years apart (he moved to another city for a job, while she stayed with us so we could stay at the same schools), however now they both say the marriage is stronger than it ever has been and both are happy in it. The cheating happened when both of them were in their mid 40s, they are both now 75. Thier marriage more than survived it thrived.
In most cases I’ve seen where one spouse has cheated there is blame on both sides. If that helps you deal with it any easier you can blame yourself to whatever extent. I’m not saying she had a right to cheat, I’m just saying it takes two people to make a good marriage and two people to make one that has trouble.
You also can’t look at cheating as the worse thing that can happen to your marriage. I used to have a friend whose husband treated her like crap but she always said that she would leave him if he cheated. Finally she left him because of how he behaved but in my opinion how he acted was worse than cheating.
And no, you won’t ever forget it. Ever. You can forgive. You can move on. You can get to a place where you don’t think about it every time you look at her. But you won’t ever forget.