Affair from my past

Back when I was 18, I started to sleep with my married teacher Alison then 29. I would see her 3 afternoons a week and sometimes at weekends. It last about a year and she and her family moved away and I lost contact with her. Then 2 years ago I met Sherrie 26 and started dating and sleeping with her, over the course of a year we became very close and decided to marry. I first met her father Albert, Bert was what he preferred and her sister Elaine 23. Her mother had divorced Bert 8 years before. Not much was said about her mother at the time and I hadn't even been told her name. As our wedding day approached, Sherrie said That her mother was going to come to the wedding as it was her grandmother Grace who requested it. Grace was very close to Sherrie and she decided to invite Alison. Alison, I was told had been in a lot of affairs during her marriage to Bert. I didn't connect straight away, that it was the same Alison I had an affair with 15 years ago. But on my first meeting her, I knew her instantly and was hoping that she didn't remember me. She didn't seem to remember me and was nice to me and had come alone to the wedding. Not bringing her latest lover as Sherrie had feared, then on our wedding day, everything was great. After our return from our honeymoon, we settled down to our married life together. About 4 months again Alison dropped by for a surprise visit, as Sherries is pregnant with our first child. She was as nice as pie as the saying goes. I work in and out of town and Alison wanted to know if I was ever in her town. I said I do go there a couple of times a year and she I should call her when I was in town and I could bring Sherrie with next time and stay with her. I said We'll see and left it at that. The next time I was in her town was last week and Sherrie was had not long had baby Grace. So we visited Alison and she met baby Grace. The day before we left, Sherrie was sleeping and I was in the backyard having a drink and Alison joined me there. She asked How I was going and did I remember her from my College days. I said I did and said I hope she wasn't going to make trouble for me with Sherrie. She answered She wouldn't make any trouble for Sherrie or me and she hoped that we would be able to get along. Then yesterday Alison called in on Sherrie and told us she had purchased the house next door to us and would be our new neighbor. Sherrie isn't all that frilled at this and I'm unsure how to proceed.