To protect his Horcrux, Tom Riddle placed the ring under a very powerful curse, so much so that Albus Dumbledore himself mentioned that had it not been for his prodigious skill, he might have died in mere moments of being cursed.
After retrieving the ring Albus Dumbledore himself fell victim to a curse that, even when contained, would likely have killed him within the year. Once rendered defunct as a Horcrux, the stone was placed inside a Golden Snitch and left to Harry Potter in Dumbledore's will.
When Dumbledore used the basilisk venom-infused Sword of Gryffindor to attack the cursed ring, it destroyed the Horcrux and disabled the curse on it. Harry Potter was able to hold the Stone without any sign of the curse affecting him thereafter.
It just made him unimaginably thirsty, which progressed into hallucinations. Yes, Dumbledore could have still survived, but remember that his lifespan was already short as it was: by putting on the cursed ring, he had a few months at best to live.
However, all of this was no match for Albus Dumbledore who was able to retrieve the Horcrux and destroy it with the Sword of Gryffindor. For his troubles, he discovered the ring to be cursed, which blackened his hand and left him with a death sentence placed upon him.
What Was The Curse On Dumbledore's Hand? + The Horcrux Ring Explained
Why is Snape the half-blood prince?
Family. Snape's family background is mostly shown in flashbacks during the course of the last three novels. Snape was born to Eileen Prince, a witch, and Tobias Snape, a Muggle, making him a half-blood (hence the name, "Half-Blood Prince").
After penetrating the outer defences, Harry and Dumbledore arrived at the island and discovered that the Horcrux was immersed in a glowing green potion. After determining that the potion could only be removed if it was drunk, Dumbledore conjured a crystal goblet and began to drink the potion.
Ultimately, it's a good thing that Dumbledore's plans didn't work out because if Draco hadn't disarmed the headmaster, Harry wouldn't have gained the Elder Wand's power when he later disarmed Draco. This was proof that, unlike Dumbledore, Harry was destined to reunite the Hallows and become Master of Death all along.
However, the Hogwarts headmaster was not a comforting character with unconditional love that Harry would want at his side as he died. Rather, as an insightful adviser, Harry had Dumbledore waiting for him in Limbo where he could choose to live or die after being “killed” by Voldemort.
Dumbledore can't bear the thought of using the Unforgivable Curses, partly because of his sister Ariana's accidental killing, but mostly because he would never willingly destroy a human being's agency.
His dad gave it to him. To elaborate on Icecreamdif's answer, he inherited it as a family heirloom dating back to Hardwin Potter, who married Iolanthe Peverell, granddaughter of the Cloak's original owner Ignotus. It was passed down to the eldest male of each new generation of Potters since then.
Notably, Voldemort appeared to be entirely unaware of this split, as he later created a seventh Horcrux in his quest to have six, and continued to target Harry Potter despite him now holding part of Voldemort's own soul.
Even if Dumbledore were to have cut off his hand, the curse would have existed within him as long as he lived. Dumbledore was around 115 years old. As powerful as he was he may not have survived having one of his limbs severed. It's also possible that he was tired of living.
Slytherins are a cunning lot, and there are all kinds of examples of Albus Potter using his wiles to come up with schemes and plans worthy of any member of Salazar's house throughout Harry Potter and the Cursed Child.
As an adult, his mastery and knowledge of magic having reached unparalleled levels, Albus Dumbledore had effectively become the greatest wizard in modern times, some even believing him to be the greatest in all of history.
Hoping to revive his dead family members (particularly his sister Ariana Dumbledore), he disregarded the ring's status as a Horcrux and put it on. This enacted the ring's deadly curse, and it began to quickly spread through Dumbledore's body, starting with the hand on which he had put the ring.
Dumbledore's lack of belief that Sirius is innocent is also suspect. Sirius was a member of the Order of the Phoenix which fought against Death Eaters, but Sirius also was as close to James as a brother, the Potters even took him in when he ran away from home.
Draco Malfoy was not the one who killed Albus Dumbledore, as Severus Snape intervened. Still, he did become the rightful owner of the Elder Wand after disarming the powerful wizard. Draco was unaware that he was the true owner of the Elder Wand at that moment and never wielded it.
Dumbledore was dying of a curse set by Voldemort, and only had a few weeks to live. If he died of the curse, that meant Voldemort had killed him and would get the mastery of the Elder Wand. If he killed himself, there was a possibility the Wand would still interpret that as Voldemort's victory.
Its effects include: Intense physical pain, extreme thirst, fear and delirium. Basically, the potion causes intense physical pain and then forces you to relive the worst moments of your life. In Dumbledore's case, the night his sister Ariana died.
The intent of the caster is a vital component of the spell. While Snape was still able to produce Avada Kedavra without any intent to kill, being a great wizard, the mix of hesitation and necessity probably resulted in the spell being blue.
