Can 2 married attractive opposite co-workers maintain platonic status even after some kissing has started?

My wife has a "just friends" relationship with this pretty good looking guy who is 7 years younger than her and 14 younger than me. He was training her on new systems at a large tech company and she came home talking about this really talented guy that's working with her. As she got to know him she admired his even temper demeanor and smooth laid back country style. ( at least she was honest enough to fill me in daily about her new friend).Every day it was "I love the way he treats his wife like a queen" or he has 2 little girls and he seems to be a good father.On her birthday he and some friends played her a song (he plays mandolin) and they had a little party. I was not invited of course as her work location with a large telecommunications business is 50 miles away. Over the months they would go to lunch in his big crew cab pick-up and I later would learn engage in these hot make out sessions. She claims that's as far as it went at this point but I also realized after more checking and talking to her previous male friend they had been going out in his truck for several months before the time she indicated it began. Already the dis torsion of facts and deceit begins. But I was cool with it cause she openly informed me of her time spent with him and ured me "just friends". This deal had been going on for 10 months or so and I found a greeting card site in our computer. After finding out the pword and looking at the 5 or 6 cards she had written I was smashed and shocked, the stuff she was saying to him was all about missing you when I'm away even a day and I wish we had met when we were little and just want to squeeze you and I love you and heres your mage token so I can help relieve you of work stress ....this was a girl smitten and ready totally consumed with this redneck Teletech. I know wife of 21years at the time and shes infatuated with her new 'BOY". She called him her sweetest thing which was at the time a movie expression for a guy with a nice package down below. Now I'm not so impressed with her lack of truth as a matter of fact I think she has maybe already fooled around. A few days later I also found a BD card she bought for him and it was one of those I'm so in love with you cards and a hat. When I confronted her with the boyfriend at work stuff she laughed and said he's just my boy and this is just puppy love. I have not had with him and we just kissed a few times in his truck at lunch.I was not really convinced and stashed the copies of the cards for later. I went to her office and talked to him in person and pretty much told him you know if I told your wife would she believe this was just kissing. He promised me he would cool down this thing and not go off alone with her anymore. I think his intentions were to stop but my wife was bitter and pissed and acted like I was invading her world.She wants to be "just friends" with him. Should I trust them?As more time went by she began to change some and was more critical of my ways I had had for years that used to be funny to her were now disgusting. Our life went from hot to cold and all info of him ceased. She had a guarded stance on any attempts I made to ask about work.Get this now this is where i regret my choices and am almost embarred; I reluctantly agreed to let them stay friends at work and it has been like that for over 7 years. I can't prove any specific took place but I know I would have a hard time making out with her and it not become pion and then . She has a nice blond and blue eyed look with a killer body and this walk that grabs your attention. I'll be honest with you I go through spells where I pick up vibes and tell tale signs of hanky panky going on. do you think given these details that it is just platonic friends or should I be worried?