Codex

I recently started seeing a guy who I am incredibly into and he seems to be as well. Last night he was going to go off to a party alone and I wasn't 100% comfortable with the idea. The main reason because a week before we got together his friend had told me that he had made out with some random girl at that party, and that he had a bad habit of doing that. Last night that same friend told me I shouldn't worry, but I'm a little conflicted and a little confused on how I should feel and how I should handle this. Should I just say what was in the past is in the past because he is with me and I wasn't some random girl. Should I let him know what our friend told me, and why I wasn't too comfortable with him going to that party. Even so how does a new girl let him know that she does have expectations without coming off as manipulative or "naggy".