In Adventure, Tai and Matt are in a state of strife; they both look to each other for validation of their point of view when making decisions but Matt is distressed by Tai's impulsiveness and believes Tai can lead the team into danger by ignoring his generally more practical solutions. As Matt feels he does not identify with Tai, Cherrymon is able to convince Matt that Tai is his enemy at one point. He also feels occasional resentment towards Tai for taking up the responsibility of acting as a role model to T.K., something Matt believes is his. In spite of their obvious tension Cherrymon is surprised to find their relationship as strong as it was and so difficult to undermine. Tai and Matt, however, reconcile at the end of Adventure.
In Adventure 02, Matt and Tai are on better terms and best friends, and when Matt punches Tai at one point, it is purely for Tai's sake.
In Digimon Tri, there's been some scenes where Matt could possibly like Tai more than a friend. In Digimon Tri: reunion, when Mimi is reuniting with the gang Matt stares at Tai with some kind of unusual smile. And at some point when Matt and Tai are fighting, Mimi states "there just like an old married couple." Then Matt and Tai get flustered at that. In Digimon Tri: confession, Matt is discussing to Tai about Omnimon and then blushes.
Then in Digimon Tri: future, Matt confesses to Gabumon about how much he cares about Tai. Sounding like he was the most depressed about Tais disappearance.
Matt and Sora become close friends in Adventure and are supportive of each other. Matt understands that Sora needs to cry and tells Tai to let her be. When Sora is trapped in the Dark Cave, Matt is able to pull her out of it from experience. Sora is notably the only female among the DigiDestined that Matt does not address with honorific suffixes, signifying closeness.
In the Christmas episode of Adventure 02, Sora confesses her feelings to Matt by giving him homemade cookies. When evil Digimons attack the concert, Matt rushes to protect Sora from falling rocks. They start dating afterwards with Matt openly putting his arm around Sora.
In the last Digimon Adventure movie "Diaboramon Strikes Back", Yamato's character profile states he is dating close friend Sora. A picture of them together is spreading around the internet - Diaboramon's message to the DigiDestined that he has returned.
In the "Michi e no Armor Shinka" Drama, Matt confesses his love to Sora by shouting "Sora! I love you!" while tap dancing to distract Boltmon, thus confusing Sora.
The epilogue, as well as confirmation from Toei, reveals that the two eventually marry and have two children. Their daughter looks like Matt while their son looks like Sora.
Matt values Izzy's abilities to process facts and relies on him as a source of information. In Digimon Adventure, Izzy seemed to be the only member of the team besides Sora whom Matt did not, at one point, act bothered by.
Matt is often annoyed by Mimi's antics, but accepts her as a member of the team. Matt gets frustrated easily by Mimi's lack of common sense such as when she withholds the fact she has a (albeit broken) compass and cooking fuel. In the original version, Yamato/Matt did not express this frustration. After Mimi showed her friends what she had in her bag, Yamato/Matt commented that she was pretty prepared for survival, and later commented that her tools may be helpful now.
It is common to see them together when they are divided into groups, as in the factory where Andromon was, or when the rest of the group went to rescue Datamon. Matt is also the one who defends Mimi's feelings after they see Whamon die.
In 02 they seem somewhat closer, Matt mentions at one point in the English Dub that he's been talking to Mimi over the phone from America.
Matt initially seems to hold Joe in contempt, frequently expressing irritation at Joe's complaining and difficult personality, but over time he comes to look at Joe as a reliable friend.
Since T.K. and Matt's parents are divorced, Matt feels he must take extra responsibility for T.K.'s well-being and becomes overprotective of him. However, when T.K. proves himself to be self-sufficient, Matt feels like he has lost his purpose, causing him to leave the group temporarily to try to figure things out.
In Adventure 02, T.K. has matured enough so that Matt is easily able to let him be self-sufficient.
Whenever Tai is not around, Matt takes responsibility for Kari, although not to the same degree as Tai for T.K. Still, he seems extremely distressed when Kari is taken by Phantomon.
Matt accepts Davis as the new leader of the DigiDestined, but does not like Davis's disrespect for his sister Jun, even though Matt is afraid of her.
Matt sees Yolei as an essential member of the new DigiDestined team. Yolei also does sound-mixing for his band, The Teenage Wolves, and her sister is in his class.
Matt sees Cody as an essential member of the new DigiDestined team, and even sees a little of himself in him. When Cody is struggling to understand T.K., Matt fills him in on T.K.'s past with Devimon and the forces of darkness.
Matt is willing to help Ken get over the stress from having been the Digimon Emperor. Matt and Ken travelled to Mexico City together to destroy a Control Spire, and send the renegade Digimon back to the DigiWorld.