Well, sometimes people can have "relationships" with these phone sex workers in that they regularly chat with each other and the guy might send her gifts and she might send him things in return, so maybe these are the panties of a phone sex worker that Chad talks to.
The thing about the whole "Chad is gay and cheating with Troy" theory, is that it's just a convenient way to get Chad out of the picture and to ensure that there's no going back for Sage since she's definitely not his type, but there has to be some sort of relationship/personal drama for each of these characters and without Chad, what is there for Sage? I've often theorised that her post-Chad drama could centre around her struggling between her feelings for the MC and wanting a relationship with him, but her logical brain is telling her that she shouldn't start a relationship with a freshman.
However, if Chad were to just be a well-meaning dumbfuck who is straight and not cheating on Sage, this could be just as dramatic because it means there's a chance they could get back together, and I could see DPC doing this as perhaps he wants people to struggle with wanting all (or most of) these girls, not wanting them to be with certain people, but knowing that they can't do either of these things and will have to make a choice of who to be with which could result in these girls being with the guys they don't them to be with.