Babygirl, this can only end badly. I am talking from the stance of the wife of a supervisor who had an affair with his PhD student. He misled her, she only saw the good side of him and I only saw the bad side. I was the neglected battered wife and just like you, he told her that he was only staying because of the kids. People like that are evil most going through a midlife crisis and you are caught in the middle. She got in touch with me to tell me everything, he ditched her in an attempt to get back with me. I told him at the start of the relationship, twenty years ago that the one thing that I wouldn't put up with was infidelity. It was a really, really horrible time. I had a nervous breakdown and had to leave my teaching job. This is almost four years later and I still haven't recovered. I found out through messages on his phone. I wasn't searching, I just happened upon them. He was very kind, loving and affectionate with her but he barely spoke to me. When he was supposed to be with his family, he was at the cinema, having meals out to posh restaurants or playing squash/tennis with her. He bought her thousands of pounds of clothing including shoes, underwear and a £500 hifi system. He never remembered my birthday or gave a Christmas present and before I knew about her, I accepted this because I thought that he was just eccentric. As I said, I am still not with him and now, he tells me that he never loved her but she was there- well excuse me for looking after my dying mum, my sick father and my young children as well as holding down a full time job. He told her 'I love you more' that cut me to the core because he had never ever told me that he loved me!
Believe me infidelity is damaging just think of the other woman.
This is an old thread, I know but this **it is always happening- I hope you made the right decisions. I have a feeling that you didn't!