“When the moon hits your eye like a big pizza pie, that’s amore!” sang Dean Martin. We all know the delicious feeling of new love, but what about the flip side? Love doesn’t always last, and its retreat can leave us bewildered, confused or downright depressed.

Even if you were raised on a plentiful diet of fairy tales, you know that “till death do us part” can be a rare thing. Even staying with someone forever is no guarantee of experiencing lasting love. But why do people really fall out of love? Is there anything we can do to make love stay? Do some of us give up too easily? To understand the phenomenon of love’s end, we asked the experts’ opinions on the subject. Here are the top three reasons they shared with us: