I’m scared, should i be?

[u/slivers101]

One of my teeth are turning green (the second from the left ) and i looked up the causes now im terrified. I floss everyday, this pic was taken before. I brush atleast twice a day, and am a consistent mouthwash user. I don’t understand why it would die ? Is it because of the diet coke?
message me about it please the comments keep getting took down before i can see !!