After Mrs. Jones reveals that she has done things she would not tell him or God, Roger realizes that they both have made mistakes and can relate to each other. This is evident when the narrator states "The boy's mouth opened. Then he frowned, but not knowing he frowned." This suggests that Roger is processing this information and forming a connection with Mrs. Jones, ultimately leading him to stay behind.

make this sound like a 7th grader wrote it

After Mrs. Jones says that she's done some secret stuff she wouldn't tell anyone, not even God, Roger has a light bulb moment. He realizes that both of them have messed up in their lives and they're kind of similar. You can see this when the writer says "The kid's mouth opened. Then he had this sort of annoyed look on his face, but he didn't even know it." It's like Roger is trying to figure out what Mrs. Jones just said and he starts feeling a connection with her. That's why he decides to stick around.