The June issue of LaLa revealed that the Marriage Purple manga will end in the next two chapters.
Furthermore, it's worth remembering that the 5th volume of the manga had already revealed that the series would end in the upcoming 6th volume.
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.
Marriage Purple was therefore launched in Hakusensha 's LaLa in July 2018.
Source: ANN