Because the nature of interest is qualitative, then there is a relative factor (depending on who the person is) in determining one's interest. Example: each person has a different ideal type of pair, beautiful / handsome is relative (ugly is absolute: p), there are more preferable to short women than tall women, some prefer a muscular man than a man not muscular, or quality- Other qualities that have different judgments depend on the person who reviews them (relative).
A person's interest can be volatile (up and down), as time goes by, everyone changes, time changes everything, someone becomes more attractive and some people become less attractive.
The conclusion is if you want to know how interesting you are, then look at the reactions of the people around you. And the important thing is that attraction is not an irreversible fate, remember that the attraction is judged as a whole (overall) then increase your appeal.