It was a big thing, yes, but it doesn't explain why he needed to keep it a secret from Natsuna. Also, just finding his old man wouldn't be worth breaking up with his girlfriend, obviously. Unless he's planning to marry his old man instead...
@Kaarme ikr! why did he need to keep it a secret from natsuna... guess author wants to raise up the -breathing intensifies- level of readers? That's the only assumption I can make from it. and here I was hoping he was trying to prepare natsuna a surprise of some sorts. OTL
@SquigglesJP Haha, yeah. I actually also expected both the sisters' men were preparing a surprise for their girlfriend. The ages old cliche of consulting another woman on what would be a good gift.
I did think perhaps Sotoyama asked Yukito to not say anything, as it would obviouly make Natsuna imagine all kinds of worse alternatives on her own. But on the other hand Yukito is kind of broken, like I said earlier, so it's believable he simply wouldn't think he would need to say anything.
If this is actually the case, then Sumeragi is really a douche for being more considerate to this little green-haird bitch, who he just met and doesn't know from a hole in the ground, than being considerate toward his girlfriend.
On another note, Natsuna really needs to bide by her own advice and confront her inconsiderate boyfriend.
The whole situation is funny because after the Mother's death (or was it the vacation?), Yukito said to both Natsuna and her sister that he wanted to look for his father. Now he is keeping it a secret from Natsuna and her family, who were supporting him ever since they started dating. But the reason is unclear. Was it because he cares for Tsuna's studies? Doesn't want to trouble the family? It makes no sense.