Found - a rare 1916 first edition of Mendel, A Story of Youth by Gilbert Cannan. The novel is a roman a clef about the artist Mark Gertler and has much on his disastrous affair with Bloomsbury Goddess Dora Carrington. The verse dedication is to her:

To D.C.

Shall tears be shed because the blossoms fall,
Because the cloudy cherry slips away,
And leaves its branches in a leafy thrall
Till ruddy fruits do hang upon the spray 
Shall tears be shed because the youthful bloom

And all th'excess of early life must fade
For larger wealth of joy in smaller room
To dwell contained in love of man and maid?
Nay, rather leap, O heart, to see fulfilled
In certain joy th'uncertain promised glee,
To have so many mountain torrents spilled
For one fair river moving to the sea.

Gilbert Cannan entertained Mark Gertler, Katherine Mansfield and D H Lawrence among others to a famous 1914 Christmas party at Cholesbury Mill in Buckinghamshire and between 1914 and 1916 Gertler was a frequent visitor. Gertler used Cannan’s shed as a studio and his painting of Gilbert Cannan at his Mill now hangs in the Ashmolean Museum, Oxford (for which much thanks).

Between 1914-15 Gertler pursued a frustrating love affair at Cannan's  Mill and elsewhere with Dora Carrington, who eventually left him to live with Lytton Strachey. Their relationship is the subject of the 1995 film Carrington*. After Strachey’s death in 1932 Carrington committed suicide.

*Rufus Sewell played a fiery Mark Gertler in the movie. Below is a sample from Christopher Hampton's script - Gertler is very annoyed that Carrington is in love with Strachey:

Mark Gertler: Haven't you any self-respect? 
Dora Carrington: Not much. 
Mark Gertler: But he's a disgusting pervert! 
Dora Carrington: You always have to put up with something.