I don't know quite what to do guys.?

My friend used to like this chick. Like head over heels. He then got her!!! For maybe a few weeks then things came to an end. This is a while later now and I'm not sure about how he feels towards her. But she flirted with me for a few days, since she's so pretty and intellectual I can't help but be attracted. With V-Day coming up and both of us available. Should I yield my friend's feelings or go in for the kill? Hmmmm.. Tough one guys!