If I remember correctly once you have corpus you are immortal but with horrible side effects - but was the Nerevarine cured of the whole disease,or just the side effects?If the latter does that mean the Nerevarine is immortal?

The Nerevarine is spared from the horrible side-effects of Corpus, but gains the benefits. Yes, the Nerevarine is functionally immortal; he/she can be killed, but the Nerevarine won't die of "natural causes."

Hmm...okay then...but I remember reading a thread where it said becoming immortal or ascending would cause a dragon break...I don't believe the Nerevarine did this,did he/she?

Corprus makes you ageless not immortal.
He/she wasn't cured of anything. Nerevarine still has and will always have Corprus. Divayth Fyr removed only the negative effects of the disease.

" does that mean the Nerevarine is immortal?" No Nerevarine can die from violence.

Immortality, in it's pure sense, means that you can't die from disease, organ failure, cancer, etc. It doesn't neccissarily mean that the person with it cannot be killed, or that they do not age. Dracula is immortal, but he can be killed with a stake through the heart.

Invulnerability means that one cannot die from violence, but can die from other means. Superman is Invulnerable (unless he's near green kryptonite.) However, he can age, and presumably can die of asphyxiation (lack of oxygen.)

Invulnerability combined with Immortality is what you're thinking of- there's no real term for that since it occurs so rarely in fiction unless we're talking about gods. When it is used, however, it is usually called Immortality- which isn't correct.

The Nerevarine is "biologically immortal" which is not true Immortality.

That's how the term is often used in fiction, but I consider it in incorrect definition, because if mortal means that you can die, then being immortal, i.e. not mortal, would mean that you can't, so a true immortal would simply not be able to die at all, a least not without exploiting some weakness, because fiction likes to give characters who would otherwise not be able to be killed weaknesses, probably because having your heroes never be in any danger would get boring, and if the invulnerable characters are villains, it would be pretty hard to stop them if there isn't some way to kill them, assuming that there is not a solution other than violence, and in any case, some examples of immortal characters who are unable to die due to natural causes or other things couldn't really be called invulnerable, as that would indicate not being harmed by physical violence, yet some characters who are considered immortal CAN be harmed by violence, it just doesn't kill them, at least not permanently, maybe they'll regenerate any injuries they recieve, or even if they're killed, they'll just come back. But that's just semantics that isn't really important here, basically, yes, the Nerevarine was not cured of corprus, as Vivayth Fyr tells you in the game, he only succeeded in removing the negative effects of the disease, things like the disfigurements, loss of the ability to reason, and such. But the positive effects still remain, in the game, the player becomes immune to all diseases after that point, and presumably the Nerevarine would also be unable to die from old age, but obviously, this isn't reflected in the game since you don't age during the game and it's unlikely that you'd play long enough to die from old age anyway. Obviously, the Nerevarine can still be killed by violent injuries, the game would be even easier than it already is if after that point in the main quest, you couldn't be killed at all no matter how much damage you took.

So in short, the Nerevarine still has corprus, but won't become a monster because of it, which works to fulfill part of the Nerevarine prophecy, which is probably why that part was important.