Having a boyfriend/girlfriend, even if nothing more than a platonic relationship is not a source of scandal. What others assume is their problem, and that assumption can become scandalous if they are spreading rumors out of that assumption.
Actually living with a person of the opposite sex, say for the reasons of affording rent, more accurately approaches scandal because right or wrong people can view this as a sign of ongoing sexual relationships. It is unwise to do because it can be a source of scandal to others. I had a friend who simply could not get it in his head as to why I would not agree to share an apartment.
He felt that as long as we knew the truth it would be fine. But I explained that it was important what other people thought; that it could damage our reputations regardless of our innocence; and that it opened the door to temptation. It is never a smart thing to do. Consequently we never lived together, and eventually our friendship ended.
Scandal can be created out of many situations, and I think usually arises out of gossip and people making wrong judgements about others. In college I was trusted in having access to all the Arts and Humanities tests of my University, with the exception of classes I was taking. I had more than one person attempt to have me get them copies of those test, which I never did. If I had, I would have created a source of scandal.
Those entrusted with a company’s monies could be stealing and cause scandal by their actions or even by making it appear that others where guilty who were in fact innocent.
So I think each act of scandal needs to be assessed on its own, and really we don’t every draw a line as mentioned here. We just have to be astute enough to know the difference.