Walter Waters the watermelon is a trustworthy but quiet person. Only major relationships or relationships with main/major characters are shown in this article. Matt and all his best friends attend the same class, a different class from Gumball and Darwin's own.
Walter is best friends with Sticky. Together they fit as a team since Sticky is knowledgeable and Walter is good at planning and strategizing. When they're not playing a sport, they talk a lot with each other and even have some debates about random things (whether its about politics, science, or why "catsup" is pronounced "ketchup").
Walter and Ronald are also best friends. They hang out with friends during school breaks and play soccer or basketball. Ronald also respects Walter highly and considers him trustworthy and a good strategist.
Matt and Walter are best buds. Matt admires Walter for his skills in planning and despite his serious personality likes to hang out with him. He also relies on Walter as a leader or a "comrade" in situations like in "The Joy Rebels." Walter considers Matt also as a good friend and is one who likes Matt's jokes. Matt also cheers Walter up and plays sports with him such as in "The Doppelgänger."
Lewis is another best friend of Walter's. In "The Watermelon," Walter "recruits" him then later befriends him. In the same episode, he (and other students) also gives Lewis a cake. Together they hang out with friends and play sports together. Lewis relies on Walter as a trustworthy friend.
Walter and Gumball have a small but okay relationship. In "The Doppelgänger," Gumball interrogates him along with his friends then gets Walter to help him and Darwin on finding then catching Clayton. They also work together to bake a cake in "The Watermelon" although not directly interacting with each other.
Walter and Darwin also have a small but fairly friendly relationship. They interact in The Watermelon where they indirectly work with each other and "The Doppelgänger" where Walter helps him and Gumball on their quest.
Bobert and Walter befriend each other in "The Dares" after the two dance off. Matt dares Walter to show off his dance skills to the crowd, and this attracts Bobert to show his dancing skills in return. Together they dance off, then later team up to beat Tobias in a dance competition. After this they go to the cafeteria to hang out.