Where did Snape's allegiance lie?

Question

From all the movies and what I have been reading on HP wikia, it is clear that Snape was in love with Lily but did not share the same affection with Harry. He only tried to save him during his years at Hogwarts because Harry had Lily's eyes and he promised Dumbeldore to do so. But he was also with Voldemort and was a death eater. What I dont understand is where did Snape's allegiance lie?

From wikia page it is evident that when the prophecy was made Snape was eavesdropping and he was the one to tell it to Voldemort, so clearly he was at that time loyal follower of Voldemort but once he got to know that the suitable candidates to complete prophecy was Lily's son (or neville longbottom but Voldemort decided to go for harry) and Voldemort has decided to kill Harry, that will result in death of Lily too thus he went to Dumbeldore and asked him to save Lily in return of "anything". Dumbeldore fulfilled his promise but still Voldemort managed to get lily so Snape now had to follow Dumbeldore's order and save Harry. So at that time was he cheating and lying with Voldemort to save Harry but was still in favour of Voldemort on any other matter except Harry?

His character was very complex I feel and I cant figure out what his mind and intentions were at various times, especially before and after Voldemort decided to kill harry (and thus indirectly harming Lily)?

Answer 1

In my knowledge both Lily turning her back to Snape after he called he mudbood and her dating and marring James Potter caused Snape to completely follow the path of becoming full time Death-Eater. After hearing The Prophecy made by Sybill Trelawney to Albus Dumbledore at the Hog's Head Pub in 1980 he was still in the Dark Lord's service, and as a loyal Death-Eater he reported his findings to his master. Although he never heard the part of prophecy saying

"..and the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not... and either must die at the hand of the other for neither can live while the other survives... the one with the power to vanquish the Dark Lord will be born as the seventh month dies...."

After realizing that Dark Lord interpreted first part of prophecy as James' and Lily's son and sought to kill them all, Snape sought Dumbledore to help him protect Harry as he was still in love with Lily. After that failed, and both James and Lily were dead, Dumbledore played the guilt card and asked Snape to help him protect Harry as Dark Lord will return one day.

Albus Dumbledore: "If you loved Lily Evans, if you truly loved her, then your way forward is clear. You know how and why she died. Make sure it was not in vain. Help me protect Lily's son." Snape: "Very well. But never — never tell, Dumbledore! This must be between us! Swear it! I cannot bear... especially Potter's son "

So in conclusion. Snape was indeed a very complex person, he made a series of wrong choices but he did work for Dumbledore since The Prophecy was told, and everything he has done since was in name of good. All from working as double agent for the Order of Phoenix to killing Dumbledore per his request and saving Draco Malfoy's soul in the process.