Season 2, Episode 9 - The White Asparagus Triangulation
Aired November 24, 2008
Leonard has a new girlfriend and, best of all, she meets Sheldon's exacting standards. When Sheldon gets worried that Leonard will ruin this relationship like he did with his previous ones, he sets out to firm up his buddy's relationship.
Season 11, Episode 14 - The Separation Triangulation
Aired January 18, 2018
Raj gets caught in the middle of a domestic dispute when he learns the woman he's dating, Nell, is still married to her husband, Oliver. Meanwhile, when Sheldon rents his old room back so he has a place to focus on his work, he annoys Leonard by being the perfect tenant.