My wife Cheaed after 18 Years

I caught my wife texting with her Co worker on Thanksgiving day. She was denying it even after I read her messages of how they made each other feel when they were together. After about an hour or so I sat her down and she confessed. Denying she had she had been intimate with him and that she only needed someone to talk to and she liked his company. Several private get together had been happening already. She would make arrangement to have all our 4 Kids busy for a couple of hours while I was at work to spend time with him. They would argue since he was pushing the relationship further and she new it was not going to last for them. He is in his 2nd marriage and has 4 kids from both marriages. She tells me he would say the right things and was always there for her when in need. She would talk about how unhappy she felt in our marriage when we would have arguments. She would also go and let him now how unhappy she was in her sex life with me. She denies being intimate with him but yet my heart tells me there is more. My 16 year old daughter was aware of this situation since she was bringing him around even to school events while I was at work. He was known as a co-worker to my kids. I had already confronted her months earlier when he was calling her in the morning, lunch and after work. She would argue that it was only work related. I know they went out for drinks and would always schedule to be together during work functions after school. I am still with her trying to work things out. I am feeling so guilty for not being their for her needs but something tells me this is wrong. I still love her so much but the fact that she did this to me is eating me up inside. She has submitted her resignation but is still with him everyday until that day gets here. She tells me she is mad at him for taking advantage of they friendship that she just wanted to have with him. She tells me how stupid she was and that I am the only one for her. I don't know how to handle this and I know there are other people out there with my same situation.

Please need advice!