Wife Cheated- Need Advice

My wife went to a college reunion where she met old friends. A guy she had fancied in the past was there and at the end of the night he offered her a lift to a petrol station where she could order a taxi. He took her to the petrol station and she ordered it. It didn't come though so they drove to another petrol station. During this time they were chatting about the past and he bought beers. She drank two of his beers and smoked his cigarette. He then drove her to a dark place nearby where he pulled his pants down- She said no- She said she would give him a hug instead and they huggged. He leaned over and kissed her on both sides of her neck and then they held hands for 1 minute. He drove back to the station- she was with him from about 11.45-2.30am when the taxi arrived. When she was leaving she gave him a kiss on the nose and gave him her mobile number. She came back and I was very concerned to know where she had been all this time and she didnt want to answer- she went to bed and i slept on the couch. Next morning she admitted what happened and after squeezing her for the details over the course of the day i got all the details(i hope). We've spent the last two days- crying, in pain, angry- giving out to her- everything and im really confused and frustrated. I feel like i can probably forgive her but its eating at me and its so painful to think of her in that car. I also found out that last year at another reunion he had walked her to her taxi. Shes not even friends with him. She was obssessed with him when she was young- like 10 years ago and use to follow him around and crave his attention cos he ignored her. My wife drank 3 large bottles two nights ago of beer and this guy gave her 2 cans so she had 5 altogether. She said she loses her mind when she's drunk but i rang her at 1 0 clock and asked her where she was- she told me she was in a bar with her friends- when in fact she was in his car and she didnt call me baby or love like she usually always does- she was dismissive and almost ignoring me on the phone- i told her to get home and hung up. I feel like i should I insisted to know where she was. How can i trust her now? She always talks about trust and how bad cheaters are but then she did exactly what she preaches. Im so shocked- I believed in my wife more than anything. I never thought she would do this- our love and marriage of 3 years is so good and happy and we get on so well. She has issues from when she is younger about being neglected its called BPD i think- but sometimes she craves attention. She says it wasnt about the guy- but she wanted his attention cos he never gave it to her in the past. SO what do i do. Please help. This is new to me and i never thought id be in this situation. Im in pain. I love my wife and wanted to grow old and we always talk about that together. How can i forgive her for this. When i think of her in that car for 3 hours with him and then him touching her wasit, kissing her neck, holding hands and her kissing him on the nose....She didnt have sex- she tells me- she said she said no- but she expected him kissing and feeling her-Im lost for words. Please help and give advice on what you guys think. Thanks