I have lost all that I love

I think they use it as a way out of something they can't even handle. I've been married was married to my girl for 9 year's. We made 3 beautiful children and before the first one was born she cheated on me with a random person that sweet talked her one day. I forgave her after a few months work on the relationship and forgave her. 3 years later she did it again and she was pregnant at the time with my beautiful daughter. Once more I forgave her. My final son was born with some difficulty and was in the hospital for 4 months ended up getting 4 brain surgeries 10 spinal tap 2 blood transfusion and he is doing better. Now that he is 1 year old she decided to cheat once more and her excuse is that I never paid attention to her that I care more about the kids and not her. I don't understand why I have dedicated 9 year's of honesty and being faithful for her to do it again and now wants a divorce. What did I do wrong? I work to provide I purchased a home and build a therapy room for my boy. I have been trying to understand her and I just can't see it. This year alone I have worked extra hours just to finish paying hospital bills and I don't even get a thank you or I'm proud of you my love no I get a sorry I got tired of waiting for you so I found someone else