Zane was flabbergasted by Emma motion. He was right about Emma being up to something. He managed to control himself earlier, now Emma was giving it away once more, but this time she was going to do it the right way.
Zane felt the urge to consume Emma immediately, after all they were married. He didn't touch her last time because they weren't married and he was against such a principle, but now that they were married, he could touch her, however Zane thought about the consequences of it.
What if Emma gets pregnant, if that happens, he wouldn't be able to be a judge of Emma's character. He wouldn't want his child to grow without his mother, and he wouldn't want to even think of splitting with the mother of his child.
Given the promise he made to his father, he would be breaking it entirely if Emma got pregnant for him, and he ended up not liking her like he ought.