That doesn't make the theory any more likely. The flashback of EP8 is further than just 3 years in the past. Also, in the flashback of EP5, we see Jill comforting an Isabella at the Preps mansion. So the flashback of EP5 can be at most 3 years in the past because we know Jill is in her 3rd year of college.
Theory of why James is gone. Isabella cheated on James with Tommy and was caught by James inflagratie. Tommy escapes through the woods and meadows and James drives the car looking for him. Tommy escapes, but James has not returned since. Why Tommy? In the same flashback, Tommy is sitting on the stairs with Rusty. Tommy's shirt is completely torn. Do you want to know why James hasn't come back yet? When he was looking for Tommy, he wasn't paying attention and hit Heather, who later rolls past Tommy in a wheelchair with two broken legs.
Now you can wonder why Jade doesn't like Isabella.