From the pilot

He was dubbed by David Hasselhoff.
His old identity plays an important role in some episodes
Episode 210: Knightmares
Michael & Kitt are looking for a stolen substance called Alidium. After tracking a suspect to the Bedford dam, Michael is caught in an explosion and loses part of his memory. He wakes up thinking he's still police officer Michael Long.
Then Michael Long's ex lover (Stephanie Mason) appeared in three episodes.
Season 1
Episode 118: White Bird
Season 2
Episode 220: Let it Be Me
Season 4
Episode 411: The Scent of Roses
With these exceptions (and obviously the pilot), his old life is virtually never mentioned. He's never expressed remorse or nostalgia. Keep in mind that the Foundation changed his face and identity
without his consent.
When they show him his new face and tell him that Michael Long is dead his reaction in the pilot is like, "Uh, okay.". He doesn't show the slightest concern for his old friends, relatives, or even his lover.
It was a different time.