Personally I would not stay in any relationship once the other person has cheated. There is never an excuse for it. I would cut my losses, get over the hurt, and move on.
Like you said, either decision is painful. You can go through a short lived pain and be happier in the long run, or cling on to hope and likely be unhappy for a very long time. In your shoes I would pick the path of least resistance.
Sounds like I've had a tough time
