The jocks are at the party because DPC needed some opponents to give the MC something to chew on!! Nothing more, nothing less!
And about Chad and Sage, it shows much about Sage and not very good things.
Seriously why did Sage choose Chad, he never was smart or very kind or gave her any sex and she is a sex freak !!
She choose him for the muscles, she loved his figure that's all and Chad took that oppotunity to hide his true relation.
So we have a girl, Sage who is mostly interested by the figure of her lovers and for the MC it's the same, he's handsome and so he became her fuckbuddy.
She is not really interested in the MC and he totally understands it, he told her he wanted more but she didn't seem to really get it.
Even when they are closer during the HOT's party she seems mostly annoyed by Chad's presence and uses the MC once again to make him leave.
So for me Sage is just a superficial girl who needs a good fuck, who fantasize on muscular men who will fuck her brains out and who hates to be rejected as a spoiled child. She wants Chad because she has decided so and she won't abandon that idea easily.
She is the female version of most MC in our games !!