I think there's a distributing spaces problem in general, not only in the separation between buttons, but also in the button itself.
The distance between the short text and the icon on such a wide button leaves unevenly noticeable blank spaces, together with the buttons layout cause a visual mismatch throughout the composition.
Personally I would solve it ...
Nathan Rabe's answer is an improvement on your idea because it wouldn't work without an explanation.
But I'd suggest you another way (seen before on digg reader - unforunately discontinued)
Instead of uncovering the actions via swipe (Cristian Negraia's answer), you can trigger the actions directly.
Swipe left -> Mark as read
Swipe right -> ...
This could work, but it will likely need additional affordances.
Be default, this does not have any discoverability: users won't know that three different actions are possible and may become confused they can't consistently trigger the desired result.
That said, if you used icons or labels to indicate available actions, there is no harm (and usually a ...
I think you can show status "Saving" under the text field when a user clicks Enter button or change cursor focus on another element. If user leaves the page just do autosave of last unsaved data. It shouldn't be too complicated.
Eventhough there're possibly many alternatives for every aspects and none of them is perfect or better over the other for each desired case, I prefer the right choice because as far as I know and experienced, human brain works grouping similar things together.
So leaving secondary buttons on the left side and leaving primary button on the right, alters ...