Boku to Kanojyo no XXX is written and illustrated by the mangaka, Ai Morniaga, since 2003. It runs in the bi-monthly magazine, Comic Blade Avarus, which is published by Mag Garden. Currently, there is seven volumes in this series. The seventh volume reached #10 on the Japanese Comic Ranking in the week of March 8-14, 2010. Each volume takes about a year or a year and a half to be published. The next volume, Volume 8, will come out probably around June 2011. Rumors has it that volume 8 will be the concluding volume of the series.
This series is also published in English under its translated name, Your and My Secret. ADV Vision published volume one of this series in 2004 but failed to published the rest. Around March 2008, Tokyopop took over and has translated five of the volumes. The next one, volume 6, will be available for purchase on August 10, 2010. The average rating for this series on Tokyopop and Amazon is around 4-5 stars.
There is also a spanish version and a chinese version of this manga, but I could not find any information about those versions.
Credit to Wikipendia, Anime News Network, and Tokyopop for the information.