The 5th volume of the Marriage Purple manga revealed that the series will end with its 6th volume, which will be released this summer.
Synopsis
The manga centers on the character Rin, who enters her dream high school and has an unexpected encounter with her elementary school classmate, Yukichi. They never got along, and Yukichi seemed to enjoy starting fights with Rin back then. When they meet again, Rin absentmindedly signs a piece of paper with her name on it, only to find it's a marriage contract with Yukichi. She promises not to submit to it on the condition that Rin "never leaves her side" for the next three years.
Furthermore, Marriage Purple was launched in Hakusensha 's LaLa in July 2018.
Source: ANN