Sounds like Noctis was close, but Prompto is making such lovley noises above him that Gladio doesn't want to pull away. After all, Prompto had done such a good job in getting Ignis off that he deserves the same.

One hand slides over a hip as his tongue catches against the rim of Prompto's entrance, drawing against it with little playful licks before pressing in. At the same time his hand curls around the base of his cock, hard and leaking to which he gives a quick squeeze.