He didn't even plan to propose. It just kind of popped out, but it was lucky that it did because now he gets to marry Jun and have a happy life.
Satoshi poured all of his love into that night and made sure that it was perfect for Jun.
One chapter to go. (If I can get my befuddled brain to write the necessary words.) Nino will make a very cute bridesmaid. Bahahah.