It started with amateur interracial cuckold videos. I was super turned on by that, and eventually I showed them to my girlfriend.
Although she did like the videos, she said she couldn't imagine doing that, and she was afraid I was looking for an excuse to sleep around myself.
After some years of fantasizing in bed together, she went out with a girlfriend of hers. In a raggae club, she got hit on by an attractive black guy. She then texted me if I really was okay if she would "play" a little. After I (happily) agreed, she made out with him and gave him a bj.
That's how it started.