a major doubt...

Not "weak" but "damaged".

The exact quote is "That boy's soul is not yet so damaged. I would not have it ripped apart on my account", as stated by Dumbledore. Remember that in the HP universe, killing rips the killer's soul apart.

Dumbledore did not want to have Draco's soul be ripped like Tom Riddle's soul was already. He wanted to preserve the boy. Dumbledore's soul or Horcruxes have nothing to do here.

Hence Severus' reaction regarding his own soul and what would happen to it if he killed him. To which Dumbledore replied that "You alone know whether it will harm your soul to help an man avoid pain and humiliation."

What Dumbledore meant is that the intention behind any action (here a murder) is the key. If killing in general maims the killer's soul (in the HP universe), it is allowed to think that killing out of mercy (in Dumbledore's case here) would not damage the killer's soul, at least not as much.

Hope the above explanation has lifted your major doubt.

No, Dumbeldore means that like, Malfoy's soul wasn't ruined as he hadn't created any major sins, like killing, you know, if you kill someone you're supposed to go to hell as you kill your soul by doing one of the major sins.

Cause Dumbeldore was cursed, doesn't mean Malfoy would be cursed if he killed him.

The quote was "The boy's soul is not yet damaged" (or something similar). He was referring to Draco being, to coin a phrase, "innocent." He hadn't killed anyone or purposely seriously harmed anyone - his soul was still in one piece and unharmed.

Draco didn't know Dumbledore was dying - if he had killed him, it would have been out of pure malice. Dumbledore didn't want Draco to go through that. He knew there was good inside Draco, but if he harmed his soul in anyway, that goodness might very well disappear. He also used it to get Severus to agree to kill him.

i dont know