It just occurred to me, that her grandma told her something in chapter 1 that made her blush. I am guessing since we don't know the context yet, that she basically told Akane to marry him since she still loves him, it's her first crush, and it's her only chance to get him, so she shouldn't mess it up.
Yet she messed it up while being married to him.
Correct me if I am wrong, but I was under the impression from an earlier chapter - the one where she was sick and he had to carry her to the hospital - that what Akane was told by her grandmother was to do with Akane going to medical school to be a doctor and her grandmother paying for it. I thought this was when her grandmother told her that if she didn't marry him she would not pay for it.
It could be a combination of what you said and the medical school thing OR at the time Akane was just not telling him the truth.
If there is more to it than what we already know then I guess we will find out eventually.