Director Greg Berlanti revealed in an interview that there were clips of the "friend group" (Simon, Leah, Abby, and Nick) that were filmed without the actors' knowledge. In order to capture the authenticity of a group of friends beyond the confines of acting, the director would sometimes tell the actors to "cut" but have the cameras keep rolling. Many of these unscripted interactions of friends just being friends (including the dancing in the car scene) made the final cut.
Jennifer Garner's "exhale" speech wasn't originally included in the film: there was just one 'parent scene', and a scene with the dad. When Jennifer became interested in the role of Emily, she asked director Greg Berlanti for a scene that has her connect with Simon, so they built it again and wrote what would become essentially the message of the movie.
In Simon's bedroom, there is a copy of Becky Albertalli's (the author of "Simon vs. the Homo Sapiens Agenda") second novel, "The Upside of Unrequited" on his bookshelf. "The Upside of Unrequieted" also takes place in the "Simon-verse" and revolves around Abby's cousins.
Although the movie is titled "Love, Simon," it was actually an adaptation of the book "Simon vs. The Homosapiens Agenda." The movie originally had the same name as the book, but it was too long to say, hence the name change.
The words "hour to hour note to note" can be seen written on Simon's wall, which is a nod to the E-mail ("email@example.com") Simon used in the book to talk to Blue. It was changed in the film to "firstname.lastname@example.org."
In the movie, Simon has a reaccuring dream about Daniel Radcliffe, who starred as Harry Potter in the "Harry Potter" franchise. On his wall, Simon has a Hufflepuff crest on it. Hufflepuff was one of the four houses in "Harry Potter."
Love, Simon (2018) marks the second time major studio 20th Century Fox has made a film that showcases a sympathetic portrayal of a leading homosexual character coming to terms with his orientation and ending on a happy note. The first was Making Love (1982) in 1982.
The trivia items below may give away important plot points.
The last cast member to be announced was Blue. Book fans spent months waiting to discover the actor who would be playing Simon's E-mail buddy. Throughout the whole of filming, no pictures were released of the actor.
At one point in the film, Martin makes a joke to Abby that you would call a Black and a Jewish person "Blewish" (or, Blue-ish). This is essentially revealed to be Blue's identity in the end - he is indeed black and Jewish.
Foreshadowing: At the start of the film Nick talks about a dream he had where he had to choose between red and blue. Abby responds that he is a cross between Cristiano Ronaldo and Sigmund Freud. Of the two people Nick asks out in the film, Leah is at this point wearing blue, and Abby is wearing red. At the Halloween party, the two people who go on to ask Abby out are Nick, who is dressed as Ronaldo, and Martin, who is dressed as Freud.
There is a scene in the film which hints that Simon's best friend Leah (Katherine Langford) may have some undisclosed feelings for Abby (Alexandra Shipp). This is further explored in "Leah on the Offbeat", the sequel to the first book, although it isn't known if that story will ever be turned into a movie.