His priority is Shinzo Abe's nightmare. He obviously likes her, yet he never truly considers any other options than leaving her behind for good. Little kids automatically follow their parens, but he's not a little kid anymore. He's a high school student. Lots of high school age students move out for various reasons. It's an extremely common thing in manga, so it's definitely a thing in RL Japan as well, to some degree.
For what it's worth, this has a
lot to do with Japanese culture's view on teenagers, to my understanding; and what little knowledge I
do have is quite outdated, so take this with a large grain of salt...
In the West, we
typically (but not always) delineate growing up as "child > teenager > adult" and we also tend to divide teenagers into "adolescent" and "young adult" to further delineate things, as a way to describe those who are closer to kids (usually 13-15) and those who are closer to adults (usually 16-18, since the age of majority is 18).
As I understand it, though, in Japan, that delineation isn't really a thing. You're either a child or an adult, with little in between; teenagers, even high school students, aren't "young adults", they're "older children". But still "children" at the end of the day and, well, you don't entrust kids with the same kind of responsibilities you'd entrust to an adult, would you?
Further exacerbating things is that Japan's age of majority is also 20, so if you're a teenager, you're
legally not an adult. It's why you rarely see manga talking about high school students getting driver's licenses (the age to get a license to drive a car is 18 and most high school manga MCs are 16-17) and part of why high school students having part time jobs or living alone becomes short hand for "complicated home life".
So, yeah, TL;DR, look at high school manga MCs as if they were all 12-13 rather than their canon age and the attitudes of them and the adults around them for why they act the way they do start to make a lot more sense (to say nothing of how Japan, like most of Asia, is
really big on the concept of filial piety).