Given what happens once Lyle returns, “get[ting] better” refers to detoxing from drugs. Eli’s innocence shines through in this passage when he’s so distraught about Lyle leaving, as he seems not to understand why this is happening. Then, calling Lyle “Dad” when he gets back illustrates how close Eli is to Lyle. The fact that Lyle isn’t related doesn’t matter—this is the man Eli sees as his father, which hints that Eli probably doesn’t have a particularly close or healthy relationship with his biological dad. Lyle then forces Mum to get off drugs too, which is another way that Lyle cares for his chosen family; he gives Eli and August two functional, caring parents.