I took it as Nozomi finally starting to realize that it isn't as normal for her to be a guardian for her lover's sibling and that she and Shino have a relationship based on codependency and that if Shino were to get a lover soon she'd be all alone.
I never thought of the possibility that Nozomi parents might adopt Shino. This could make for a great ending. Would in that case Shino have Nozomi`s last name and Nozomi Shino`s