A a few clues from the film:
When Peter's mom is dying she makes a few references to his father she says young Peter looks just like him, and also describes him as an Angel, composed of pure light.
At the end of the film when Nova Prime is telling Peter he's only half human, she says his father is something "very ancient" they hadn't seem on Xandar before.
Finally, as the Ravagers are leaving Xandar, Yondu makes a disparaging remark about Peter's as to why they didn't deliver him as a child as they were paid to do.
So piecing that together: Peter's father is an ancient character (or race but the comment was worded pretty carefully to suggest his father is ancient), looks like Peter, and while good hearted is also possibly has some questionable character
Who fits all that?
Eros of Titan (AKA Starfox) . A few key facts:
Is a member of the race of Eternals, and younger brother of Thanos.
Has red hair, which both young and old Peter are shown to have in the film
From the description of Eros:
While his brother was captivated by Death, Eros loved life, and began visiting other systems for adventure and romance. Eros even visited Earth at least once, and was remembered in Earth's legends.
His primary power, aside from being an Eternal, is being able to stimulate pleasure in other beings... or pelvic sorcery in other words.