The story in this issue is A Love So Lonely. This story originally appeared in Famepress' Juliette Picture Library #3:
In between Juliette Picture Library #3 and Unforgettable Love Stories #11 Page Publications published at least 3 editions of this story, each with a new Chatto cover:
Love and Romance Library #267
Romance Experiences Library #2
Lovers World Library #9
Lovers World Library #9 was reissued after Unforgettable Love Stories #11 as Lovers World Library #12:
There may be more Page Publications editions of this story. Note that none of the covers above are swipes of the original Famepress edition. It's probably too bland for Chatto to get his hands dirty but he may have swiped it after all. TBC.