
I think you misunderstood the character. It's not that he doesn't want to be understood by his family, it's just that he doesn't care anymore. They made him cut all emotional ties when he was ostracized, and now he has just grown up into someone who doesn't need them. Moringa has been constant in his comments about his parents: "I don't want to go", "I prefer not to see them again", etc, etc.

This is not the first time he's tried to talk to his parents. This is an ongoing saga with his parents that has lasted for 10 years. They have treated him badly this whole time and you're acting like he owes them anything.
It came out that he was gay when he was in his first year of high school that he was gay and his parents believed the rumors that he caused Masaki to try to kill himself. They pretty much gave up on him them. They agreed to pay for his school only to get him out of their hometown so that people would stop talking about him and thinking bad of the family.
So that's 3 years of high school treating him badly and refusing to knowledge that he was gay, all 5 years of college just paying for his college and refusing to talk to him more than they had to, and 2 years of him being a working adult and never talking to him until they decided Kunihiro wasn't giving them grandchildren fast enough so they'd try convincing him to be straight one more time.
His mother might be willing to listen now, but after 10 years of being a shit parent, he doesn't have to give that to her.
Morigana is being selfish, yes, it's you vacation, so what, that is your mother! She is trying to understand YOU! But the only thing you can think of is yourself? Yes you don't have much time to see each other, boohoo, there will be other vacations, it's not like your mom will go through this more than once.
I guess you don't care if your mom and dad get you, or is ok with you being gay? You just want to be alone with him and forget about everything else, If that's the case Morigana better never whin about them not accepting him being gay, them not understanding, them never talking to him again and all that messed up mess.