Antinous was a constellation near Aquila, but is now part of it. There is no mythology associated with Antinous as it is based on a real person, a teenaged male lover of the emperor Hadrian, who drowned in the Nile about 130 CE near what is now Mallawi. The actual reason for Antinous' death is a matter of conjecture, but at the time it was viewed as a self-sacrificing effort to protect the life of the emperor, who had received portents concerning his own fate. Hadrian was deeply affected by the loss of his companion, and established a city (Antino÷polis) in his honor, near the site of the drowning. He also created a constellation from a group of faint stars to the south of Aquila, the Eagle. That region had not been previously considered part of any constellation, but as a result of Hadrian's decision, when Ptolemy wrote his Almagest (16 years later) he mentioned Antinous as a southern extension of Aquila. The mythology of Aquila includes the Eagle's kidnapping of Ganymede, and historical maps of the constellation show Ganymede clutched in Aquila's talons in the same place where Antinous once lay (though not "attached" to Aquila). Though Antinous remained a constellation for nearly two thousand years, the overlapping representations of Aquila and Ganymede with Aquila and Antinous led to its being discarded when the IAU established the modern list of official constellations in 1922.
Historical Maps of Aquila and Antinous
Aquila kidnapping Ganymede, from Bayer's 1603 Uranometria
(Image Credit: USNO copy of the 1661 edition of Bayer's Uranometria)
Aquila and Antinous from Hevelius' 1690 Uranographia
Note that as for Argo Navis, Hevelius' maps are reversed left and right relative to Bayer's
(Image Credit and © Tartu Observatory Virtual Museum; used by permission)