"Even if Lucas is fine with it, if he knows he will tell others. And we don't know how they will react.

Not because he can't keep his mouth shut," but he wouldn't discount that; Lucas doesn't strike him as a person who won't discuss things with people close to him or chatter away when he gets nervous, "but because the more people know, the more likely it is that even more people hear." And he'd prefer to tell others on his own terms. If he does at all.