Kitto Aishite Shimau n da.

From ShoujoHearts:

The protagonist, Ayumu, was secretly dating her superior at her company until he broke up with her. Though deeply hurt, she could not outwardly express it. Not long after, she began living with her well-liked co-worker, Yachi, at her grandfather's house. While living with the friendly Yachi-kun, Ayumu starts to change..