The flame that burns the wax from the candle.
When you think about it, the very phrase "spend time" is rather romantic. Sure it's idiomatic, but think about the meaning of the words. To spend time. It's actually quite poignant of a phrase. Time, is like money. It is spent on the things you care about, the things you truly desire... but time is the most important asset we humans have. To spend time with someone, is to burn away your life with someone you truly care about. To waste away your minutes with someone. It's quite a grand gesture; you'll never get that time back. Even if you were to be stripped the clothes off your back, you'd have your time. It's part of us. Intrinsic in nature. Using it is an expression of love, be it a platonic love for friends or family, or romantic love. Maybe that's one of the many reasons it hurts so much when someone uses that time against us; the thought that all that time was for naught.