Most Helpful Guy
He flirted and she gave him her number? Dumping her was smart. I'd say it's only appropriate for a guy to exchange numbers with a girl in a relationship if it's important, like a school assignment or a coworker that needs to call just in case. Flirting and giving a number means now you're going to be wondering if he's texting her on the DL and such.
She's only good for a hookup now, otherwise, avoid.