She says coworker is a friend

My partner of many years became close to a male worker she would go out for lunch with him and they would chat all the time at work, he would text her at all hours, she used to work in a bar and he would text her in the early hours of the morning, he knew when to text and when not to.

I got suspicious and got into her mobile phone account and noticed she had text me 10 times during the day but had text him 75 times on the same day she would ask him why he hadn't texted her and where was he going to be at this time and that.

So I set up a recording device at home and went out leaving it recording, lo and behold on the recording I could hear her talking to him like he was her boyfriend and talking about going away for the weekend of her birthday to meet up with friends who lived in the city 300 miles away, I knew these people already but it seemed he did too, and that he could book the Friday off so they could travel to the city together that evening, she was talking about his mum and his sister like she knew them, and even mentioned that she wouldn't be able to wear anything sexy next week because the weather was going to be cooler.

.all this was presented to her from me and she denied anything was going on..finally she admitted that she was falling for him because he complimented her and treated her nice and he was someone new even though she'd known him 4 years.

My question to her was did she sleep with him she says she didn't but with no way of proving this I can only take her word for it..and that's kinda where I am at the moment not knowing whether she did or not..

Any thoughts would be appreciated.