
I don't know...
Yes, vacations come once a millenia, longer the older you get, but I think that it's silly to not give up his vacay this time.
Logically, if he focuses on this issue now, then he will up the probability for significant change within his own family and possibly even his quaint little town. Making younger folks who were just as scared and confused as him have an understanding ally to turn to.
And, yes, the mother's late blooming is a wee bit selfish, but the opportunity for change within a human, let them be old or young, is way too rare and valuable. It's okay for her to be selfish in these moments, because she's changing her way of thinking, her emotions, her relationships, her very being so that she can learn and grow some more. And that’s amazing. That's something I will happily support and waste my very rare vacay on.

You are entirely correct, but I am still highly irritated because if I was in long distance relationship with someone like Souichi I would count my days to spend time with them. And also as reader I am very judgmental of his mother, so I am not going to forgive her for another ten volumes until she does something beyond being timidly interfering.

Oh, yeah, absolutely don't just immediately forgive her! She doesn't deserve automatic forgiveness for what she's done to Morinaga. I def support her new perspective on everything, but it doesn't mean that she holds any of my respect.
As for the relationship aspect. Yeah, that's understandable! I've never been in a relationship myself, but I know that if I had limited time to see my significant other throughout the year, and someone who I usually have a bit of a beef with came along and interrupted that time, I would be hella pissed! But, if it was for a reason like this, then I would be way less pissed and more "About fricken time!" and call it worth the wasted time. But I get where you're coming from! It sucks either way!

You are giving the "potential ally" too much hope too, I think Morinaga's reservations about trusting her are realistic considering how his life has been, I think in this manga everything is going to come out okay, because is an overal positive story, but, Real life??? They not always become allies, and even if you keep holding your hopes up for them to understand just to at the end say "Oh sorry I think I can't accept it after all but I hope YOU respect MY decision of not supporting your life choices" ,that coming from your own family hurts more than anything in the world.
I feel so irritated on behalf of Morigana. Vacations are hard to come by, as much as Tatsumi family is generous his mom’s late blooming acceptance is at the selfish.