Artemis and Kid Flash are both former members of the Team, but from different backgrounds. He comes from a legacy of heroes, while her family consists only of criminals. After months of antagonism and quibbles, they eventually grew closer to each other, and ultimately formed a relationship that lasted up until Kid Flash's death.
Artemis and Kid Flash were introduced to each other on August 8, 2010, at 19:55 EDT. Days before their meeting, Artemis had saved Kid Flash by distracting Amazo with an arrow. Before that, she had only seen him in the news. Kid Flash, unsurprisingly, had no idea who Artemis was.
Their first meeting went poorly. Unaware that there would be a briefing or a new teammate, Wally arrived at the Cave in swimwear and carrying beach gear. He tripped over his parasol, to Artemis's amusement. He was embarrassed and became hostile–repeatedly questioning who she was and openly stating he'd prefer Red Arrow to be the Team's archer, causing Artemis to become even more defensive.
Verbal sparring and other prospects
During their first mission together, Kid Flash blamed Artemis for everything that went wrong. Even after Robin pointed out she had saved his life a week before in their battle against Amazo, Kid Flash refused to give Artemis any satisfaction. Though the mission was a minor success, Kid Flash had to be forced to thank Artemis and welcome her into the Team.
Neither showed any overt romantic feelings toward the other, instead focusing their attention on their teammates, Miss Martian and Superboy. Artemis had liked Superboy since the moment she first laid her eyes on him, and made no attempt to hide her feelings. Kid Flash's attempts to woo M'gann were slightly less subtle, but much more frequent and, as Robin put it, bordering on creepy. He went out of his way to impress her, to Artemis's apparent frustration–especially after his lies nearly killed everyone on the Team during a mission in the Tower of Fate. Noticing his relationships with both girls, Kent Nelson advised Wally to find a "little spitfire" that wouldn't let him get away with anything. Though he considered Kent's advice, he kept his attention on Miss Martian.
Second first meeting
Their hostilities witnessed a brief turn when both were lost in the Bialyan desert, their memories of the last six months blocked by Psimon. Their new "first" meeting went off far friendlier than on August 8; Kid Flash tried his best at flirting with her. Because she did not know that she had become a hero, she suspected she was sent out to kill him by her father. Since they were alone with no one else to help them, they cooperated to evade the local military. When they finally encountered a teammate, Miss Martian, Kid Flash quickly and emphatically denied any knowledge of M'gann–even calling Artemis "Beautiful" as he did so. Miss Martian offered to restore their memories, but Kid Flash had to convince Artemis to participate, taking her hand.
Upon restoring their memories, their surface animosity returned; neither was able to let go of the other's hand quickly enough. She denied having had any feelings for him, claiming that when she spoke of killing him, she was thinking about a movie she had seen, about a ninja girl whose ninja father ordered her to kill her ninja boyfriend, who was from a rival ninja clan. Kid Flash pointed out that this would make him Artemis's "ninja boyfriend", but she was quick to remind him that at the time she had had no memory of how annoying he was. Kid Flash said she was equally annoying, at which point Robin told them both to get a room.
Though never expressed directly, Artemis and Kid Flash did show some affection for each other. During the Team's battle with the Injustice League on October 1, the pair watched each other's backs closely, and Artemis was quick to tend to Wally's broken arm. In no place was it more visible than in a telepathic training exercise on October 16. In a simulation of an alien attack, Artemis's "death" visibly upset Kid Flash, and completely robbed him of his ability to think straight. At first, he vowed revenge, but when he found traces of Zeta radiation in the aliens' weaponry, he held the hope that he could still save her—and the others, as he was quick to add. When the mission was over, he avoided Artemis. In the therapy sessions held in the aftermath, Black Canary questioned him why he was so distraught over Artemis's "death", which caused him to nearly choke and vehemently deny any feelings–though he did not protest when Canary told him he was in denial. Artemis, on the other hand, was primarily concerned about her family secrets, something she did not want anyone, especially Wally, to know.
On Halloween, a casual question from Zatanna made Artemis realize Superboy and Miss Martian were together. She was upset, and though Zatanna took her on a girl's night out to help her get over it, Artemis refused to discuss her feelings.
Wally still had dreams of striking up a relationship with Miss Martian, unaware she was already in a committed relationship with Superboy. He desperately tried to score a kiss off her on his birthday. Artemis took it upon herself to inform him that M'gann was off the market. Wally was disappointed, but he soon became preoccupied with a mission.
Towards a relationship
Red Arrow finally joined the Team, to Wally's joy and Artemis's annoyance. She already felt insecure about her position in the Team, after her mother implied there was more to her induction than just saving Kid Flash's life from Amazo. Artemis was eager to prove herself a good archer, and volunteered for the next mission, tracking her father, Sportsmaster. En route, Wally told her she had already proven herself a valued member of the Team. But the thought of her secrets being exposed caused Artemis to do foolish things. She misled her teammates, tricking them into following a tracer she planted on a passing train so she could intercept Cheshire, her sister, on her own. Her ruse was discovered by Red Arrow, and after the failure of the mission Wally blamed her, calling her "insecure and selfish". He thought her desire to upstage Red Arrow had cost them the mission.
Weeks later, he was still mad at her for failing the mission. He reevaluated his views when she finally revealed her family secrets to the Team–the real reason she went after Cheshire alone. He stood by her side in support, a reaction that boosted Artemis's confidence.
After defeating the Light aboard the Watchtower, Kid Flash took the stroke of New Year as an opportune moment to pick up Artemis in a bridal carry. When Artemis kissed him, both agreed they should have done that a lot earlier.
Wally and Artemis stayed together over the next five years, and moved to Palo Alto where they attend  and adopted a dog. At some point they retired from heroics. Wally made a habit of forgetting Valentine's Day, forgetting four in a row before finally remembering in 2016.
 Though he was not averse to putting on his costume in an emergency, Wally was not happy to see Artemis go on such a dangerous mission. Following Artemis's faked death, Wally spent time comforting her mother, who credited him with getting her through the tragedy.
Wally worried immensely about Artemis's safety; after the undercover Aqualad and Artemis blew up Mount Justice into smithereens, he confronted Nightwing. Although Nightwing trusted Kaldur'ahm, Wally has started to have doubts about Kaldur being a triple-agent.
The pair were finally reunited after Artemis's deep-cover mission ended, with Wally returning as Kid Flash to aid the Team in bringing down the Reach-Light alliance. When devices unleashed by the Reach threatened to destroy the Earth, Wally and Artemis worked together to defuse a device planted in Paris. The pair were tragically separated when Wally "ceased to be" during the speedsters' last effort to save the world. When Wally felt his body disintegrate, he asked his uncle to tell Artemis, as well as his parents, that he loved them.
In the aftermath of Kid Flash's death, Artemis rejoined the Team, but as Tigress in order to cope. She felt that her "Artemis" persona was Wally's partner, and she needed to distance herself from that part of her life. She also went to tell Wally's parents of their son's sacrifice.