Most Helpful Guy
You do it because you get something out of it, possibly the thrill of the attention it gets you from the people you tell the secret to, or the power thrill of being able to expose someone's secret.
Since you're dating a drug dealer, we already know your moral compass is fucked, so either of my two reasons seem likely to be true.
Most Helpful Girl
You can, but you don’t respect that person enough to keep their secret. You can build your respect for others first in order to keep a secret.