Why has she done this???

I have been in this relationship for 8 years and we are planning to get married this year. I live with the woman and thought we were both happy. She shows no signs of discontentment, and I am experienced with that, being married before and having a long term relationship previously. I have to tell the story of how I got to this point first as that will help you to understand. Our sex life went down hill when I moved in nearly 7 years ago. She is not comfortable when her two boys aged 25/28 and one live in girlfriend are in the house, so we had weeks and even a couple of months go by without getting together. We got to a point where we just accepted it, but lately I decided something had to be done. So when we could afford it we went away for the weekends and our sex life started to get back on track. We started to go back to our old ways of having fun in the bedroom and being naughty to heighten the excitement. It was all good fun. We joined a adult web site that that you could post pictures up of yourselves, although not our faces you understand. We got loads of attention from other users sending private PM’s. And this was exciting and our sex life just got better and better. You can save other users profiles and have chats and so on. It even helped my partner to gain more confidence and we found way’s around the problems at home, great. Now this is the weird bit and not what you are expecting. We had a PM from some guy, he had pictures that were not very good and I was ready to discard his pm’s but my other half said she wanted to keep them. We wrote back and it got quite saucy to say the least, again a bit of fun. We got to a point were we swapped emails (web mails) to swap more pictures and I asked him for a picture of himself, we also sent him one of us. Now I’m not sure what it was, I think his email address was familiar, I’m not sure but I got a little suspicious. I checked my partners email and found his address and some emails that she had sent. Mainly forwarding funnies, I get lots from my brother. The earliest email dates back to June last year! Way before we started on the adult site. So I now know that she knows him. Why they took this risk I don’t know, but I feel like I have been used for a joke, I feel totally betrayed. Anyway, there is nothing much in these emails and the only ones that have me worried are one that she sent to him with her CV attached and a simple message saying (Here’s my CV you asked for xx) another forwarding a web site saying (Hello gorgeous lover here’s the web site) and 5 emails she sent him with no message but with 5 photos of our holiday last year to Turkey. These photos were all of her three of them lying in the sun with in her bikini. I think she forgot to delete all these emails, I found them doing a search, aol keep all your emails unless you delete them. I got into her hotmail account and his address is there as well, but I found no emails. I am wondering if she message’s him. I have said nothing to her yet, with great difficulty, but I have installed a key logger on to the computer that only I can access. It takes screen shots and logs all key strokes and messages; I did this five days ago. All I have detected is that when she comes home from work and last thing at night she logs on to her windows messenger and on to his profile. But so far no messages have been detected. She also logs on to his profile on the adult site every day as well. I am not sure, but I think she might have his mobile number; in fact I am pretty sure of it. She does not got out in the evenings and there is no sign of at all of her doing anything else suspicious. We went out tonight, and she was as she away’s is to me. In the pictures tonight we held hands, she was caressing my hand, and leaning over for a kiss now and then. She tells me that she would never want to be without me and loves me loads. I don’t under stand it at all. Even if she is not having an affair, she has hurt me so much I just feel like dung. I really thought I had found the right person. We are both in our early 50’s and looking forward to spending the rest of our lives together. Sorry this is so long, but I would love to hear from anyone who can help, or just have an opinion. Am I doing the right thing?? I just want to be sure I know what is happening, that is why I have kept quite and watching what she is doing on the computer. I feel if I speak to her now, it would be difficult to believe any defense that she offered, and if she swore she had not been to bed with him, how could I be sure. The trust has been broken, so I need to know positively that she has not committed the ultimate sin. Thanks for reading. W.