"Why would I betray her? She's got her priorities in the right place. She's useful until we're the last ones left."

For the most part, that's true. Howard knows how Diana thinks. Better the devil you know than that you don't, and where Diana goes stashes of supplies are sure to follow. She's an asset up until the point she tries to kill him.

"Up until the end, we have a mutually beneficial relationship. I'm smart, she's smart, together we're double-smart."