The plot thinnens.
Potentially, but most likely no? Without some development, the plot could easily stall at this point. But if Aika confesses, suddenly Riko is in a terrible spot. Her ability to see herself as a good person is contingent on her lolicon-ness being an affliction she is trying to cure, not an intrinsic feature of her personality. If she accepts Aika's confession, her self-image collapses, and how she develops or regresses from there is anyone's guess. If she rejects, Aika is going to have to confide in someone to cope. If she confides in her sister, then Riko's best friend now knows she's a lolicon and probably into her little sister, turning every conversation into even more of a mine field. If she confides in her school friends, then who knows who they might tell and how the story might mutate in the retelling, wreaking havoc for Riko in other ways.
Whichever way it goes, I expect glorious chaos.
So I hats gonna happen to this forbidden romance when Aika ages up considerably in 2-3 years will Riko just lose her appetite?
This would be so good (in the very plot-twist funny way. like, you are too big now, byebye) but nah, these stories tend to forget (or wasn’t the intention at all) that the MC is attracted to children after they fall in love, it’s more like they can only start relationships with children and then forwards it’s ok if they grow up
Sorta. A lot of these sorts of stories don't have the protagonist actually be a lolicon at all, with the protag's one unfortunate age gap relationship being depicted as a one-off event. The character may have an "Am I a lolicon now?!" panic attack, but ultimately decides those fears are unfounded when they fail to have the same reaction to other children. Of the ones where they are textually lolicons, many of them are short/oneshot thin books where the aftermath isn't really considered. In the rare few cases where I've seen a story about a lolicon in a serious, long-term relationship (most of which are Itou Hachi tbf), the older partner gets off less on the literal age of their partner and more of the extreme difference in age and power. Depending on the exact ages involved, they have a good 10+ years before that disparity equalizes in any real way.
To be clear, "they can only start relationships with children" isn't...wrong, exactly? But it's not a unique situation, either. It's pretty common for people to realize that partner is no longer within their usual strike range, but the preexisting romantic devotion can persist regardless so long as both parties continue to nurture that connection.