It is there straight from the first episode when they're both colleges student, and goes all the way until the end, at episode 38 (combining both series + the 2 ovas), when more or less 5 years have passed, their lives have taken different paths, and he's together with another woman, whom he loved from the beginning.
Even at that point, even if she has a man supporting her (Nomiya), her wound for that unrequited love still hasn't healed yet, and the impression is that the scar left in her is consistently big, and perhaps designed to remain in her forever.
The whole unrequited love of Ayumi is one of the most poignant situations I've seen in anime. Because the world of H&C feels real, henceforth the pain of Ayumi. Mayama tries his best not to hurt her, but it's simply a damn cruel and painful situation for both of them.
And to follow Ayumi's love (dis)adventures was really hard, because everytime is like hitting the head against a wall while running. I always hoped something may have changeg, I always rooted for her... but at the end, reality stayed as crud as it was. Any lights of hope that occasionally turned on, were blown away like a small feather in the strong autumn wind.
There's a fantastic confession scene at the end of episode 6, when Mayama is carrying her at home (she's drunk), and she keeps saying him "suki ... dai suki ... suki .. dai suki" while crying her heart out. Mayama stays quiet and only interrupts her with "Ah... hm.. arigato.. hm" ... under a melancholic starry summer sky.
That scene is legend, one of the best anime scene in the whole anime context; no wonder why Ayumi is my favourite Honey & Clover character
