I hear it all the time: "I'm just dating him in the meantime."
It reminds me of something Pablo Picasso said to aspiring artists: "Never take a part time job because it will become your full-time life."
Dating "in the meantime" is based on the belief that time is infinite. But in reality, "in the meantime" is wasted time, which means missed opportunities. Sure, you may be living in the moment, but it's a moment that has been dulled around the edges, stripped of importance and immediacy. When you're living in meantime-mode, you're constantly letting yourself off the hook and embracing a reactive approach to life rather than a proactive one.