Lily and Robin
Lily says in Arrivederci, Fiero that they became best friends by keeping a secret together.
When Lily returns from San Francisco, Robin is the only one who supports her and even helps her to find an apartment. Robin was also the maid of honor at Lily and Marshall Eriksen's wedding, which further proves their friendship. Likewise, Lily was the maid of honor at Barney and Robin's wedding.
Lily often says that she has a crush on and lesbian dreams about Robin. They have kissed three times so far throughout the entire series. They kissed in Rally, The Broath and Best Prom Ever. In The Perfect Cocktail, it is shown when Lily drinks martinis, she tries to kiss Robin. In The Broken Code, Lily chases away a woman named Amanda at the Farhampton Inn bar in case she became Robin's new best friend after she and Marshall move to Italy; her breaking point in making the decision was in fear that the woman and Robin would engage in the strictly sexual lesbian relationship she had been secretly coveting since meeting Robin. In Rally, after failing to wake up Barney multiple times, Robin suggested that she and Lily should make out hoping it would wake Barney up, which got Lily excited. This was the first time Robin suggested that they should make out instead of Lily.
In the last scene of Rally, their roles were somehow reversed as Robin is now the one wanting to make out with Lily while Lily is now reluctant because her kiss with Robin earlier in the episode felt weird to her, and Robin even said that it's "stupid, so stupid...", the same phrase Lily used when she wanted to make out with Robin.
- Purple Giraffe - Lily and Robin meet.
- The Wedding - Robin confides in Lily that she is in love with Ted.
- Best Prom Ever - Lily confides in Robin that she hasn't achieved all her dreams and they kiss.
- The Scorpion and the Toad - Lily meets and catches up with Robin after she comes back from San Francisco.
- Arrivederci, Fiero - Lily and Robin recall how they became best friends on a Thai food trip with the Fiero.
- Ted Mosby: Architect - Lily helps Robin track down Ted when she suspects him of cheating on her.
- Something Borrowed - Robin acts as Lily's maid of honor at her wedding.
- I'm Not That Guy - Robin finds out about Lily's shopping addiction.
- Woooo! - Lily and Robin have a night out with other girls.
- Definitions- Lily tries to get Barney and Robin to have "the talk".
- Say Cheese- Ted notes that Robin is Lily's best friend, but she began as one of Ted's "random skanks", Lily countering that Robin is the "skanky exception to the skanky rule".
- Unfinished - Lily helps Robin get over Don whom she sees on the TV.
- Glitter - Lily is concerned about getting left behind by Robin because of her own enthusiasm over trying for a baby.
- The Perfect Cocktail - Lily and Robin try to work out the appropriate drink to make Marshall and Barney make up over their fight.
- The Best Man- Lily tries to convice Robin that she still has feelings for Barney and should talk to him.
- The Rebound Girl- Robin tries to convince Lily and Marshall not to move to Long Island.
- The Drunk Train- Robin reveals to Lily and Marshall that she will never be able to have kids.
- The Broath- To seal the broath, Barney makes Lily and Robin kiss each other.
- The Broken Code- Lily helps Robin get another girlfriend, however, Lily gets jealous and drives her away.
- Rally- They try to get Barney to wake up and later they kiss. At the bar Robin tries to make out with Lily again.