In the "Higgs Boson Observation", Sheldon hires grad student Alex Jensen to review his childhood journals for any potential ideas that might win him a Nobel Prize. After Amy and Penny observes Alex and Leonard in the Caltech cafeteria talking, Penny, although having reservations about her relationship with Leonard is bothered with the thought of him with another woman. Later that day, Alex comes home with Sheldon to work in apartment 4A where Leonard and Penny are. Penny introduces herself to Alex (subtly implying that Leonard is hers) and drags Leonard to her apartment to have sex. Penny finally does admit her love to Leonard, in " The 43 Peculiarity ". Penny and Leonard awkwardly stare at each other before running off in opposite directions. Leonard, though, is buoyed by optimism over Penny's admission. Alex Jensen asks Leonard out to dinner in "The Egg Salad Equivalency", which boosts Leonard's ego because two beautiful women are interested in him, however, Alex's interest makes Penny insecure. Leonard later confirms his commitment to Penny and reassures her that nothing will happen between him and Alex. After another dispute with Sheldon, Leonard tries to move in with Penny in "The Spoiler Alert Segmentation", however, she is not ready. During their Valentine's Day dinner in "The Tangible Affection Proof", Leonard again tries to propose to Penny and she cuts him off quickly. She admits that she is very happy with him, but she also admits to commitment issues and the thought of being married forever really "freaks" her out. Leonard then tells her that when she is ready to get married, she can propose to him. In the season finale, Leonard leaves for an overseas job for four months and Penny is confident enough in their relationship to wait for him. In " The Gorilla Dissolution ", Leonard and Penny become engaged. Throughout season 8, a running gag is their reluctance to decide upon a wedding date. In the season 8 finale, Penny asks Leonard to marry her that night in Las Vegas. Leonard happily accepts, but during the journey, after Penny expresses happiness that they will get married while knowing everything about each other, Leonard confesses to having shared a drunken kiss with another woman while on the boat in Europe, though he adds that the woman started it and he rejected her. Penny becomes hurt by the revelation, and even though she claims to forgive Leonard, there is clearly tension between them, leaving the season ending in a cliffhanger as to whether or not they will go through with the wedding.