Usotsuki Paradox.

Shunsuke has fallen for his colleague Hinako, but she is engaged albeit in a long-distance relationship. She and her boyfriend meet on the odd weekends. She feels lonely at times. When one evening they are both working late and still in the office Shunsuke throws caution to the win, reveals his feelings, makes a pass and plants a kiss on Hinako. Things should make their natural progression from there if nature takes its course, but then again they chart a different course.