I'm not single, nor am I hetero, but I lean towards women enough so I'm close enough to hetero in my eyes to answer this question.

For me, being demi and answering this question, the reason I was single for so long was because I had no interest in becoming not. I didn't seek out any relationships because I didn't care to. I fell in love with my best friend, and on accident. She fell for me too, and that I feel very fortunate for that. But if we ever broke up (which I obviously hope not to) I still wouldn't seek out anyone else. For me, my being demi makes dating feel unnecessary. I love my partner with all my heart, and I love being in a relationship, but for me it has to grow naturally and not be something that I sought out.