i know i get jealous when i see my boyfriend flirting with other girls, and a lot of people ask me why i just let him do that. simply because i find no need to control him. he is his own person and i trust him completely (with everything minus one.)
he is a great guy and though i know he likes to flirt openly with other girls, even when he is right next to me, i know he loves me and wouldn't cheat on me. though only you can discern his actions and come out with your answer. if you feel that it was just harmless flirting and nothing at all... then no need to worry. though if it bothers you dont let it sit there. i'm sure it will happen again and if you don't talk to him about it... it will eat you up inside and then tons of problems ensue.
there is nothing wrong with having friends and meeting people of the opposite sex.
also talk to him let him know what kind of relationship you want to be in and find out if he wants the same. if he wants to be in an open relationship let him know your feelings on that, and if your in an exclusive relationship then talk to him and let him know that you were just curious by his actions....
do what feels right to you and act appropriately on it. your the one that knows him best here and can decide what his actions mean...
good luck!