To keep is as short as possible here is what happened to me.

Went out with a girl at almost midnight for a walk and drinks. Before we went out she told me that she have to be home early. We went out and she didn't actually paid attention at all to the clock. I had to call the walk off because i had to rest and we went home. She has a boyfriend.

Should i cease contact with her or should i ask her out again and escalate? I'm wondering because what would made a girl with boyfriend to go out with some guy late at night alone? Never really went out with a girl who have BF till this point so i'm clueless.