Sometimes, i think the master didnt mean to hurt the doctor. The Master liked him and the fact he was also a timelord, but he just never knew how to show it. And when the Doctor pointed the gun at him, He was hurt because he was worried that because of all the hurtful things he had done, that the Doctor didnt like him, and was about to kill him. The Master knew that the end of the time war was hell, and he didn’t want the doctor to have to go through it all again. So he sacrificed himself, sending him (and Gallifrey) back into the time-lock. I never felt like the Master was truely evil, he just was never taught how to express his emotions. THAT IS WHY I LOVE HIM.