A soulache, is not very unlike a headache, however, the intensity is much more ferocious. Its pain endured when your soulmate is not by your side, is away, or has gone away. A connection between soul mates is so intense and so strong, that to separate two soul-mates leads to physical and psychological pain.
Anthony is so in love with SNO, that when she is gone for even one day, his soulaches. the soul ache leads to physical symptoms like stomach pain and / or heart pain.