Responses
In regards to the ending, the way I see it, it's not so much heartbreak, than it is disappointment. It's his first ever "relationship." He doesn't know what that feeling is. He even literally asked "is this what heartbreak feels like?" No, it is not. Heartbreak is followed by depression. As someone who was rejected and dumped a few times already, I'd know the difference. In short, he wasn't that emotionally invested in Miki. That, again, is the way I see it.
That's it? So we got a poor kiss while lil bro is still going through a heartbreak from that bitch and it just ends like that... well it could be worse so I'm not gonna complain any further. But it's not the best incest manga