What should I do?

Mmk. So here is the situation. Its kinda complicated, idk, but yeah anyway. So me and my bf have been going out for a year and a half as of tomorow. Anyway a situation occured a while back with this girl that goes to our school (we are in high school). Anyway she was friends with my bf but hated me and always talked **** About me and basically tried to make my life a living hell. Which she was pretty good at. I told my bf i dint like him talking to her so he says ok i wont. Like amonth later i go on his myspace (because he lets me and gave me the pword) and i see that they have been emailing back and forth all summer talking about hanging out behind me back. So of course i got pissed. My bf told me he wouldnt talk to ppl online anymore. So today i log on to his gaia (once again he let me ) and found out that he emailing back and forth with this guy he doesnt know. So my question is, should i bring it up with him or just drop it. Is it worth a fight over? Cause im sick of arguing it.