Did I tell you my roommate's girlfriend moved out? I think I should talk to my roommate and change the way we split the rent.
I didn't know that. Why do you want to change the way you split the rent?
Now that there's two of us, it should be split in half. That means he'll have to pay twice what he was paying.
I think that's fair. Now that there are two people are your residence then the rent should be split between the two of you 50/50.
If she's not living here and contributing to the rent, he should make up her share.
I agree, it's reasonable for him to pay his half of the rent now that she is no longer there to pay what portion she was previously. I'd just talk it out with him and I'm sure he'll understand and agree.