Actually, Myers that was a joke. However I think the game called let's diagnosis Dexter sounds fun. Your diagnosis isn't that accurate. Here is why.
http://www.minddisorders.com/Py-Z/Sc...-disorder.html
DSM-IV-TR specifies seven diagnostic criteria for schizoid personality disorder:

• Avoids close relationships: People with this disorder show no interest or enjoyment in developing interpersonal relationships; this may also include family members. They perceive themselves as social misfits and believe they can function best when not dependent on anyone except themselves. They rarely date, often do not marry, and have few, if any, friends.

Dexter is very dependent upon his relationship with his sister, speaks to his dead dad and was in love with Rita. He was a pretty good husband (you know...except for the all murder stuff.)

• Prefers solitude: They prefer and choose activities that they can do by themselves without dependence upon or involvement by others. Examples of activities they might choose include mechanical or abstract tasks such as computer or mathematical games.

Nah..he always seemed to be hanging out with someone.

• Avoids sex: There is typically little or no interest in having a sexual experience with another person. This would include a spouse if the affected person is married.

At first he didn't like sex...then decided he did.

• Lacks pleasure: There is an absence of pleasure in most activities. A person with schizoid personality disorder seems unable to experience the full range of emotion accessible to most people.

He seemed pretty into the sex.

• Lacks close friends: People affected with this disorder typically do not have the social skills necessary to develop meaningful interpersonal relationships. This results in few ongoing social relationships outside of immediate family members.

OMG Dexter has a million friends.

• Indifferent to praise or criticism: Neither positive nor negative comments made by others elicit an emotionally expressive reaction. They don't appear concerned about what others might think of them. Despite their tendency to turn inward to escape social contact, they practice little introspection.

Not really.

• Emotional detachment: Their emotional style is aloof and perceived by others as distant or "cold." They seem unable or uninterested in expressing empathy and concern for others. Emotions are significantly restricted and most social contacts would describe their personality as very bland, dull or humorless. The person with schizoid personality disorder rarely picks up on or reciprocates normal communicational cues such as facial expressions, head nods, or smiles.

Dexter is so empathic he could be a therapist...if he decided to give up his serial killing hobby that is.