In the October issue of Kodansha's Afternoon magazine, there was an announcment from Riichi Ueshiba that Mysterious Girlfriend X will end on September 25.
For those who are new to Mysterious Girlfriend X, here is a summary written by our wiki editors in Anime Vice:
Akira Tsubaki was just living his normal school life until a strange girl named Mikoto Urabe transfers into his class. One day, without thinking, he tastes the drool left behind on her desk at school and becomes ill the next day. Urabe pays Tsubaki a visit at home, and using the same drool he tasted before, seemingly cures him. Urabe tells him that it was love sickness and that he has fallen for Urabe, and has become dependent on her drool. From then on, the two start to form a bond, discovering that their drool can transmit feelings and other things between them. Tsubaki soon finds himself with a very mysterious girlfriend.
Check out the Mysterious Girlfriend X Discussion.
Please check out the List of Manga Series Ending in 2014 which I'm compiling for 's Top Manga Series of 2014. It's a current work in progress.