Well, a plotline might involve Chuckie and Tommy exploring their relationship in a more grown - up world. Maybe they go on a trip together and during that time, they realize how deep their connection is. Or perhaps there's a situation where they have to work together on a project, and that proximity makes their feelings for each other more intense. There could also be a plot where they are reunited after a long time apart and the love that was always there resurfaces in a new and exciting way.
In some 'All Grown Up Chuckie Loves Tommy' fanfiction, the plot could center around the changes in their friendship as it turns into love. For example, Chuckie might be shy about his feelings at first and Tommy could be oblivious. Then as the story progresses, they start to notice the little things about each other. There could be a sub - plot where their friends either support or try to interfere with their relationship. And maybe there are flashbacks to their childhood that contrast with their current situation, highlighting how their relationship has evolved over time.