Holy crap, the comments on this chapter are dumb.
She clearly stated that she wasn't interested in him, and the ex told him that she probably considers him like a big brother now. They clearly entered this marriage with that in mind, and he told his family about it as well.
Under those circonstances, at least from his point of view, trying to do anything sexually to her would be like forcing her against her will. She hasn't stated that her feelings have changed yet, and she didn't really change her demeanour when in front of him. In that situation, with the feelings he has, the desires he has for her and her usual naivete, sleeping besides her would be torture for him.
Also, she's of marriageable age. It says, at the beginning of the manga, that she went to "Middle School", which should probably be "Junior High School" in Japan. So she was at least 15yo, and that was when an grandfather was still alive. We don't know exactly how long ago that was, but since it was stated that the granddad died a year prior to the events of the manga, she was at least 16yo before marriage.
Here's the page from chapter 1:
I would think she was probably older than that before getting married, maybe 18, probably more.
This is an awesome manga, cute, touching, with nice art and interesting characters. I've checked the raw for the next volume (volume 3) and it doesn't seem like there's much in terms of drama (there's a false cliffhanger, but nothing bad).
There are 5 volumes available, so pretty much 50 chapters, and I can't wait to see what's next. I just hope this gets a bit more views, and doesn't get dropped again 😀