Struggling with insecurity

I am male, married since 2007, one son and upto this point have always been absolutely 100% secure in the relationship with my wife. We work at the same company but different locations on the site. She works in a 2 person team her and her male boss who is single and they travel about 4 times per year usually with others from the office, groups of 4/5. I've always encouraged this and think it's great for her to travel. However, after a recent night out she didnt get home until 3am. Which is quite late for her. She told me that her, her boss and a couple of her other work friends stayed u till 230am then left. However, in a conversation with one of those other people it turned out that just her and her boss stayed until 230am everyone else left at 130am so she lied to me. It then transpires that he made sexual advances towards her, touched her leg, told her she was beautiful etc. She then said that she told him that he was obviously very drunk and they got a taxi together via his house which isn't exactly on route where he then asked her if she wanted to come up for coffee! She says she declined and they hugged, he tried to kiss her she pulled away and she came home..... I was devastated when I found out particularly that she stayed on her own with him and almost put herself in such a vulnerable position. I also work with a lot of these people and I feel like a complete mug. They are planning another trip abroad soon (5 days) I'm not sure I can hack it and she keeps saying she did nothing wrong and that he was out of order but just drunk and nothing like that has happened before. I also found out that on a previous trip she stayed out until 2am with all the guys but she told me she was in bed pretty early. She says it shouldn't be a problem staying up until 2am drinking?? When she now goes out without me it tears my stomach apart and I completely lose control of my emotions. Part of me feels like getting out of the marriage but I love her a lot, want to trust her again but not sure if i can and they are still working together and want to socialise together etc..... Any help gratefully received. Thanks