<p>Flirting can be especially dangerous if it's with someone you see frequently/are good friends with. It's one thing to be approached by someone in a bar and flirt back when you have no chance or intention of meeting them again. It's another thing to have close friends and maintain flirtatious relationships with them.</p>
<p>I don't know that I'd all it "immoral", but if you really care about your girlfriend, try to avoid flirting. Not only is it misleading, but it gives people the impression that you aren't fully committed to your relationship, which tends to blur boundaries of acceptable/unacceptable behavior. It's also not very nice to do to her - actions speak louder than words.</p>