I think you do not seem quite ready to forget this person and so, you press the last flower left from this relationship. I wonder if, in 20 years time, if it falls from your book will you remember who it was from?
I've been re-reading this piece a lot, finding the right words to comment but still haven't been able to string together the right ones. I think what I most enjoy about this senryu is the questions that arise after reading it. Like why did the character preserve a memento of what seems to be an ending (of a relationship ?), why was the book barely read, did it remind the speaker too much of someone? did the speaker just did not care for the book? what does the red flower represent?
a lot of quesetions, none of them answered but it gives a great glimpse into the speaker's relationship with that person. well-written :)