Girlfriend cheated on my with colleague

A little while back me my gf had a rough patch, to the point where I stayed away for a few weeks. This is the first time anything like that has happened during our long term relationship so I was rather upset about the situation, not her, she seemed to rather enjoy it.

She is one of the only females in a heavily male dominated work and gets a lot of attention from her colleagues, never more than this, so she said. However, when I was away she gave a lift home to one of her male co workers, a guy about 10 years older than her. She dropped him home and they chatted for a little while outside his house and she said he kissed her out of the blue, she said she pulled away at first but felt herself getting wet afterwards. So she continued to kiss him, they got very passionate with the kissing, tongues and he groped her tits and ran his hand up her skirt and rubbed her pussy over her panties. She also briefly got his cock out of his pants and jerked him, she said she also kissed the tip of it but didn’t end up sucking.

When she first told me this I was horrified and felt betrayed, however, the more I thought about it the more it turned me on, I have now got her to recite the experience while she tosses me off