Bokura ga Ita, Koishitagari no Blue Recommendations
Both Bokura ga Ita and Koishitagari no Blue involve a love square --- two guys and two girls are all in love with someone who loves someone else. The main female protagonists are "used" by the main male protagonists as fake girlfriends. The male protagonists seem outwardly happy and joking around; they secretly undergo emotional anguish from the memory of previous loves.
The chemistry between the male and female lead is profound; however, complications arise and lead to misunderstandings. In addition, both works give off a feeling of yearning with just the correct drop of angst mixed in.
Main characters start with a 'he's so annoying' attitude toward the guy, naturally this changes and love blossoms. Main guys have ex girlfriends who complicate their relationships. Both manga address first loves, and moving on. BGI is a tad more serious (and longer), but both manga have comedic aspects to them.
Both manga are as good as each other, you're more likely to cry at BGI and laugh at KNB.
Average girl meets a friendly and upbeat yet mysterious boy who is trapped in the past. She experiences first love with him and goes through turmoil and drama. Both tales tell love stories about moving on, loneliness, true love and everlasting friendship.