I got kissed by my boyfriends best friend I've never seen him in any other way than as my boyfriends friend so when he kissed me it came as a shock but then why did I actually enjoy it. Is it because I wasn't expecting it? I want to tell my boyfriend what happened obviously but I don't even know how to bring it up or explain that I actually liked it.
You liked it because it was unexpected and because you already liked the guy as a friend, it felt good to know he was attracted to you and maybe a bit because it was "naughty". The bottom line is that you boyfriends buddy was VERY inappropriate in kissing you. Think about if you liking it had to do with what I said or if you are not into you current boyfriend any more. Either way, it shouldn't happen again while your with him and you should most likely tell your boyfriend that it happened. You want to control that info and not let someone else spill the news to him.
You probably liked it because it was unexpected, new, and different. I mean, you've been kissing the same mouth for however long and this new kiss was like an infatuation. Still doesn't make it okay. Your boyfriend's best friend sucks and you need to tell your boyfriend what happened.
Let's try to overcome the hurdle of telling him that you and his best friend shared a kiss before telling him that you liked it.
For me, I consider kissing a form of cheating. Better than emotional cheating. But still cheating. A lot of my friends don't consider it cheating at all. So find out what his take on this stuff is. It will help you with how to approach him.