Leonard and Penny First Breakup

Leonard and Penny's first serious relationship begins in the season three premiere, after Leonard returns from a three-month Arctic expedition. It ends when Leonard tells Penny he loves her and she realises she cannot say it back. The breakup leads Leonard to date Raj's sister Priya for much of season four, creating tension in the group and jealousy from Penny; in the fourth season Penny admits to Bernadette and Amy during a game of truth or dare that she has not moved on from Leonard.