Identity of S... in "A Character"

The poem refers to my great-grandfaher's first cousin, Thomas Sunderland, who was a friend and contemporary of Tennyson, Monckton Milnes and Arthur Hallam at Cambridge and a keen debater. Sadly, soon after going down, he suffered a breakdown from which he never recovered. He died in 1867. See T.W. Reid's Life of Lord Houghton, vol. 1, pp. 74-6