I'm going to leave my roommate with most of the rent
Why are you going to make them pay most of it? Did you discuss this with them before hand?
No. And I'm not going to, the asshole never even thanked me for paying half of the rent
It's understandable to not be happy with wanting to pay bills but its rude to expect thanks for fulfilling your obligations. You should do what is expected of you otherwise people won't treat you equally when the time comes to.
I don't care, I just want to get back at them.
I understand that it hurts to not be appreciated, but I think it'd be more wise to not do the same thing to them. Both of you are living there, and what if he doesn't pay up? Don't you want to stay in your property?