Back story:

My husband, our 17 year old son, 6 year old son, 2 year old daughter and myself have been living at our home for the last 8 years. A year ago a family moved in and I immediately clicked with the wife because they also had three children (8, 4 and 2). My 16 year old son would play outside with her kids and our younger two all the time and we all got along really well. My son had offered to help her with some yard work and stuff as her husband worked long hours and she said that was fine and had been paying him for his help. About 6 months ago she confided in me that she was having marital problems and that her husband was moving out and a few weeks later she filed for divorce. My son has been helping babysit in the evenings so she can work because as a newly single mom she needed to work and doesn't have much help. Well, the last month or so I've noticed that they are acting different around each other and my son has been acting different, too. I asked him what was going on and he finally told me that he had sex with her! I asked her and she admitted to it as well. I don't know what to think any more. It's not illegal in our state, the age of consent is 16 and he will be 18 here in a few weeks but still...I just don't know how to process this. How would you feel and what would you think of this were your 17 year old son having sex with a 26 year old?