He was good at heart all along. However, he started off as a Death Eater. After Lily Potter was killed, he resolved to protect her son Harry in cooperation with the "good guy," Dumbledore. This was because he was secretly in love with Lily Potter.
No. But he works for the 'Light Side'.
yes
I believe you mean Snape, as in Severus Snape. Yes, he was good. Harry finds it out after Snape's death in Deathly Hallows.
Yes, in the end, it turned out Snape had been working with Dumbledore the entire time.
In my opinion the biggest secret is that Severus Snape is good.
Good and bad are subjective terms, people do both good and bad. Severus Snape certainly wasn't without fault - he did a lot of bad things, but he also did a lot of good things. Snape joined the death eater initially, but was later instrumental in destroying Lord Voldemort.
He was in love with Harry's mother, but Voldemort killed her. Snape decided he could at least help avenge her instead of letting her die in vain.
He can never be considered a good person but he did fight for the Order of the Phoenix rather than the Death Eaters.
Voldemort and his Death Eaters. He used to hate Severus Snape before discovering he was on the good side. He used to hate the Malfoy's before they changed sides and before Narcissa saved his life.
I think he came out as being good Dead. Bitter. Hopeless. Angry. Sad... etc
No, Snape is the half blood prince. His mother's name was Eileen Prince, who was a witch, and his father, Tobias Snape, was a Muggle. In Harry Potter and the Half Blood Prince, Snape admits this to Harry.
Yes, he has been on Albus Dumbledore's side since 1980 when a threat was made on the life of Lily (Evans) Potter.