This goes for Facebook and just about all social media. It's silly for guys to get all worked up about flirting on there - whether they are amped because they are flirting with a woman they like or they are upset because their girlfriend is flirting with someone. So many silly relationship dramas come about all because of some little thing that happened on Facebook and when you look at it from a rational perspective, it was really much ado about nothing.
Personally, I don't bother with social networking. It's kind of hard to play the field and have social networking accounts, because it's inevitable that women you date are going to interact with each other and I've found the BEST way to handle it is to just not have an account. But if you do have one - don't make it more important than it really is.