Knowhere

The seemingly lost man in the middle of nowhere, on Knowhere (yeah, laugh at that all you want) drew no attention from anyone that passed by, with his disheveled, unclean looks, likely a homeless man. But to Gamora, deadliest woman in the galaxy, something about him drew her in. Like she could sense something within him that nobody else could.

Or, Alternatively: Peter is homeless and Gamora takes him in. Bonding ensues. Appearances by the other guardians we know and love but mainly starmora. Oh yeah celestial peter