Is it okay to IM new people of the opposite sex all of the time when you are in a serious relationship?

He goes to a coffee shop regularly and met a new girl there, he says she is just a friend, okay fine; my problem stems from the fact that he has only known her for a couple of months, I have never met her and she IM's him all of the time. Does she realize he has a girlfriend? If so, why does she show such a lack of respect to be IMing someone else's boyfriend so frequently? In my mind girl code says show respect for the other female. I guess perhaps I am just a little out-dated, or maybe it is this compiled with hearing about the exes (or the fan club as I like to call them) so much that I am uber sensitive.