"Young Johnstone" (Roud 56, Child 88) is an Anglo-Scottish border ballad that exists in several variants.
[1] The ballad tells the story of a woman killed either by her brother or lover, depending on the variant.
One of them kills the other: often, the brother's reason is that the other has refused to marry his sister but intends to keep her as his mistress.
In all variants, the surviving man seeks refuge with the heroine, confessing to having killed her brother or her love.
She remonstrates, and he promises to get her doctors if she lives out the hour, but she tells him the wound will be mortal before then.