Grooming is a very serious and unacceptable topic. Fanfiction should promote positive values. So, I would not be able to point you towards any 'Good Omens' grooming fanfiction. There are plenty of other great 'Good Omens' fanfictions out there that explore the friendship, the adventure, and the complex relationship between the two main characters in a proper way.
There is no place for grooming - related fanfiction in a healthy fandom. 'Good Omens' has a rich universe that can be explored through proper fanfiction. For example, fanfictions that focus on the two characters' different perspectives on heaven and hell, or their experiences in different historical periods. These are much more worthy of exploration than any unethical content.
Chapter 827, "Mystical Event Investigation Bureau", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Jiang Li's words indeed make sense.
Chapter 911, "You Have Three Children?", is the clearest early answer because it turns Aunt Wan's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Jiang Bufan stood still, with his eyebrows furrowed, as if he was...
Chapter 692, "My Ideal Type is Assistant He", is the clearest early answer because it turns Gu Shengrong's situation into a concrete plot event. The chapter turns that into something concrete by moving from Zhao Lang's gaze stayed fixed ahead as he gripped the steering wheel...
Chapter 904, "Welcome Young Master and Young Madam!", is the clearest early answer because it turns Jiang Shixu's situation into a concrete plot event.
Chapter 20 is the strongest chapter-level answer because it starts from Several people turned their heads upon hearing the sound and saw three... and follows through on So, he turned and questioned Jiang Li..
Chapter 623, "Turned into a Little Crybaby", is the clearest early answer because it turns Jiang Cheng's situation into a concrete plot event. Early on, Jiang Cheng woke up again, this time realizing he was being carried....
Chapter 884, "Master?!", is the clearest early answer because it turns Senior Brother's situation into a concrete plot event. It opens with I've heard this temple is quite magical, but why are there so many... and closes on After all, Master often goes on retreats, leaving the teaching to the....
Chapter 607, "Confrontation Head-On", is the clearest early answer because the buildup finally cashes out in a real clash. A useful checkpoint is the way the scene starts with Several boats hadn't yet crossed when they were directly capsized.
Chapter 812, "You’re Extorting Money!", is the clearest early answer because it turns Bu Fan's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Jiang Li actually called the police!
Chapter 732, "Sister Xiao Wan, I Don't Understand", is the clearest early answer because it turns Jiang Cheng's situation into a concrete plot event. The chapter gives readers a real answer by opening on Bai Lu, eavesdropping in the corner, marveled at Jiang Cheng's...