Terminator: Katherine Brewster? Have you sustained injury?
Kate Brewster: Drop dead, you asshole!
Terminator: I am unable to comply.
Terminator: You are terminated.
Kate Brewster: How much did you take?
John Connor: Enough.
Kate Brewster: Well, this is the stuff we use to chemically neuter dogs.
John Connor: No, you shouldn't exist. We took out Cyberdyne over ten years ago. We stopped Judgment Day.
Terminator: You only postponed it. Judgment Day is inevitable.
John Connor: Tell her who I am.
Terminator: John Connor is the leader of the worldwide resistance and last hope for mankind.
Terminator: Your levity is good, it relieves tension and the fear of death.
John Connor: The T-X, can you find a way to destroy it?
Terminator: Unlikely. I'm an obsolete design.
Terminator: John Connor. It is time.
John Connor: Are you here to kill me?
Terminator: No. You must live.
Terminator: She'll be back.
Terminator: I'm back.
John Connor: Do you even remember me? Sarah Connor? Blowing up Cyberdyne? Hasta la vista, baby? Ring any bells?
Terminator: That was a different T-101.
John Connor: What, do you guys come off an assembly line or something?
Terminator: Exactly.
John Connor: Oh man, I'm gonna have to teach you everything all over again.
Kate Brewster: I hate machines.
Kate Brewster: Next time bring a clue, not a paintball gun.
Kate Brewster: Just die you bitch!
Answer: The difference there would be suicide vs sacrifice. In T2, basically what he meant is he could not commit suicide as it was against his programming. They had beat the T-1000 and had won, but it was too dangerous for Terminator to stick around and knew he had to be destroyed. But he could not purposely do it to himself as it was an act of suicide. However in T3, it was a sacrificial move. The goal of his actions was not to destroy himself, it was to take out the TX and prevent her from reaching John. He had to do this by any means necessary and made a sacrifice play by shoving his core into her mouth and blowing them both up. It wasn't suicide this way, it wasn't self termination. He was taking her out but caused himself to be collateral damage.
Quantom X ★
Also, after watching that scene again, I'm adding this little tidbit. The Terminator didn't actually die from the thing he did to the TX in that move. If you notice towards the end after the nuclear bombs go off, the fall out ash is falling down around its head and its eyes are still on, slowly fading away. It was badly damaged by its move, but the bombs in the end finished him off.
Quantom X ★