According to a source, "nothing really [bad] happened" between them. "They just barely saw each other the past few months and it died out."
Less than a month ago, Kardashian confirmed her relationship with the Houston Rockets player was "good" and she was traveling to Texas often to spend time with him.
The pair began dating in July of 2015, and the following month, Kardashian threw Harden a massive 26th birthday party with many celebrities, including Kim Kardashian's husband Kanye West and fellow NBA players, in attendance.
Harden then nobly stuck around during Lamar Odom's health crisis when Kardashian remained at this side in the hospital for months after he was found unconscious in a Nevada brothel from a drug overdose. It was a tough time for Kardashian since she had to juggle strong feelings for both men and divide her free time between them.
Kardashian previously told E! News that Harden was "really supportive and really understanding" during the whole ordeal with Odom. Kardashian just tried to communicate well with Harden and constantly ask what he was or was not comfortable with.