Harry had friends. He had Dumbledore. He had the teachers and many adults in the Wizarding World who looked up to him. Snape had no one. It is made quite clear in the novels (not just DH) that when Snape was a student, the teachers didn't particularly like him, including Dumbledore. He also didn't have friends other than Lily or the random DE that used him. As for affection, Harry received affection from both parents as a baby. And though he may not remember it, it still had an impact on him. He knew he *had* been loved greatly. Snape never had that sense.