Interrupted Declaration of Love

Alice has been in love with Bob but has been working up the courage to tell him. When she finally does, she manages to get out "I" before something cuts her off.

Unlike Can't Spit It Out or Aborted Declaration of Love, this trope is when a declaration of love is cut off by something outside the character's control. Usually the audience will only hear the "I" while the "love you" is left unsaid. It might even be left unclear as to whether or not the statement even is a declaration of love at all.

The interruption might come from a Moment Killer. In more serious instances, it might come from the character losing consciousness or dying. If two characters have had a lot of UST then this can be a good way for writers to taunt the fans.

Comics

 * In Empowered,

Live Action TV

 * In The Sarah Jane Adventures, Clyde is trapped on a spaceship running out of air. He records a video for his friends and, addressing Rani, says "I always...always..." before he loses consciousness.
 * in the Doctor Who episode "Doomsday". She manages to spit it out, but he gets interrupted. Ouch.
 * On Zoey 101, this becomes somewhat of a Running Gag for Chase, who has been in love with his best friend Zoey since the day he met her. He tries valiantly several times to tell her how he feels, only to be interrupted--usually by the friends who keep telling him to reveal his feelings. Ironically, for all the times he tried to tell her on purpose, he ends up telling her completely by accident.
 * The Professionals. Bodie and Doyle are driving a New Old Flame of their boss George Cowley to the airport after she's survived an assassination attempt, and she begins to say, "Tell George I..." before being drowned out by a police siren. She doesn't repeat herself, and the two debate afterwards what they should tell Cowley. They decide not to mention the comment.

Manga

 * Ranma One Half: Ranma Saotome pretty much makes it his mission to interrupt and shoot down all of Ryoga's attempts to confess to Akane. For hilarity, Ranma is usually in drag, acting like a girl, and just being a Manipulative Bastard in general.
 * In Cardcaptor Sakura this seems to be what is happening with between Touya and Yukito with Nakuru constantly butting into the conversation on purpose at the exact point that it seems that confession is about to take place seemingly as she fancies Touya herself. It's actually somewhat more complicated

Video Games

 * In Solatorobo, She says she hasn't been able to feel happiness or love in years, but has finally begun to feel them again with him. He says he's got something he needs to say to her as well, but then . She decides she'll just be patient and wait until he can tell her himself. Of course, that was Merveille's plan all along.

Western Animation

 * Avatar: The Last Airbender: Toward the end of the second season, the Gaang splits up and Aang decides it's finally time to tell Katara how he feels. He manages to get the word "I" out before Sokka unwittingly jumps in and gives him a noogie.
 * My Little Pony Friendship Is Magic has this in "Secret Of My Excess", with Spike about to tell Rarity he has a crush on her... and Rarity herself interrupting him.
 * It happens again in "Hearts and Hooves Day", with Cheerilee's "You have something stuck in your teeth" moment.