I do know what you are going through. My H went away for a long weekend and told me it was to be by himself. of course, it wasn't. He took a nice little trip with OW. And I was aware for at least one full day that he was with another woman and I just had to sit home and wait.
How you handle this is completely up to you. confront, don't confront. That is your choice. In my opinion, it is just as well that you have already confided in her sister and mother. No point in hiding her wrongs from them. It doesn't help you any. And it just makes her affair easier. So that is out in the open.
Keep in mind that you have 2 young lives to think about. You can be all upset for yourself, but the kids are counting on both of you to act like adults.
Affairs are upsetting and hurtful. But they are not the end of the world. There can be life after an affair if the two of you choose that. Many couples go on and have good marriages after healing, and many divorce. You are at a crisis point. My suggestion is that you get some advice from someone you trust, perhaps a priest or therapist, who can help you form a plan for how you will deal with the crisis.
