There is an online shopping site that I'm essentially stealing from.
What exactly do you mean by essentially stealing?
We were having an issue and pissing each other off. Because of this I'm considering stealing tons of items from them.
It's okay to be angry, but stealing is stealing no matter who it is from. You are being unfair to this store, and what if they're just a small independent store? You're really thieving from honest and hard working people who just try to live.
They are not honest and they're liars.
It's fine if you don't like this merchant, but stealing from them is flat out wrong. I think the better idea would be to not do business with them in the future and move on. Also, do you really want to risk the legal consequences of stealing?