What makes a love a tainted love? Well if you fall for someone you shouldn’t, that might mean it’s a relative, or to some people in different cultures someone of a different class, or an underage person. Your heart wants what it wants, and there’s not a lot you can do about that other than deny the feelings and go without and suffer and pine, which as most of us know is no fun.
If it’s feelings for an underage person, hopefully you can wait, they won’t be underage forever, but it can be difficult to suppress feelings, but just think of the consequences otherwise, no use being in jail and ruining your life. For some countries like India that have a caste system, it is just not acceptable to be with one outsideof your class, it seems wrong, but they have odd societal methods over there to say the very least.
As for family members, I guess as long as everyone is over the age of consent and you both keep quiet about it and make sure no children result, you might as well have it I guess, though a life of such secrecy might be difficult to maintain long term. There have been “tainted loves” ever since the beginning of time and I doubt that will ever change, it’s just the nature of people to get embroiled in dramas of their own making and torture themselves for it. Some will literally kill you with their “honor killings” if you get involved with someone not deemed appropriate.