痴情 is a noun describing a deep, often unreasoning, infatuation or devotion — typically one-sided and steadfast to the point of appearing foolish. The word carries a romantic and slightly tragic flavor; you will often see it as an object (一片痴情 'a wholehearted devotion') or in a predicate-like construction with 很 (他很痴情 'he is very devoted'). It's more than simple 'infatuation' — it implies loyalty through difficulty or rejection.