Hachimitsu ni Hatsukoi, Chicchai Toki kara Suki dakedo Recommendations
If you loved 'Hachimitsu ni Hatsukoi' then you must check out this manga as well. They are based on the same idea - the main female character falls for her childhood friend, but he is unaware of that. There is also the element of the rival girl/boy appearing and the pain of a one-sided love. The boy in 'Chicchai Toki kara Suki dakedo' realizes sooner that he is in love than the one in 'Hachimitsu ni Hatsukoi', however, they are both clueless at the beginning, so if you are into childhood-friends-fall-in-love plots, you might like this one too because they are almost the same.