Yes you can watch all previous episodes on the CW.com
You can watch all The Vampire Diaries episodes at the curirca website
The Vampire Diaries originally airs on The CW. If you go to the website cwtv.com you can find episodes of The Vampire Diaries. To find entire seasons of The Vampire Diaries check out Netflix.com and Amazon.com.
You can on YouTube in parts
hulu has them but only the last 5 episodes
Episodes 13-18 are available on Hulu
At the link below you can watch episodes 5,7,9,10,11,13,14,15 and 16
Hulu, or the CW website
youtube might have them or the network web site
If you have hulu plus you can watch it there. if not download the free CW episodes app to watch it
The Originals is a spin off of the Vampire Diaries, but you do not have to watch the Vampire Diaries first in order to be able to keep up with the plot.
Go to the website found in the related links. They have full episodes of The Vampire Diaries.
Cablevision and channel 11 need to reach an agreement. I am a loyal customer for years and a fan of the Vampire Diaries and other shows