Just wondering what y'all think...

My boyfriend and I have been dating for almost 7 months now. I have never been the type of person to keep much contact with people that I've hooked up with before. My boyfriend feels differently on the latter and has stayed in contact with some guys he's hooked up with in the past on Facebook and other forms of social media. In the beginning of our relationship, he went into detail on the sexual activities he would engage with guys before meeting me and now I am uneasy and uncomfortable when I think about my partner being with other people. How common is it for people who are in relationships to remain friends with people they've hooked up with in the past and to stay friends with them when they are in a relationship? I am curious as to how the community feel about this and to hear your opinions/experiences.