Late Nights at the Store and Lonely Hearts

It's been months since I opened up about this last time. You see, I work retail, nights, in a part of town where some people think twice before walking alone after dark. The store closes late, often leaving me to myself as everyone else goes home. It wasn't always like this, but lately the solitude has turned into something more, longing, perhaps? Last week, someone new showed up on my shift; a customer who lingered long after I rang up his items. We talked about everything and nothing, but mostly just looked at each other for an extra beat before he left. Since then, it's been this game of late-night flirtations that seem to happen every time we're both there. It sounds silly, really, just glances and small talk over the counter, but it feels like something more. My partner knows I'm non-monogamous, but how do I bring this up with him? Or should I even try? What would you guys suggest?