The Set-Up (2)

Section 2054 of State S's penal code prohibits carrying concealed weapons unless one reasonably fears an attack from an enemy. D is charged with violating §2054 by carrying a derringer pistol. At trial, D proposes to testify that W, his wife, told him confidentially before he armed himself that she was having an affair with X who loved her so much he was going to kill D.

The prosecution objects to D's testimony. W, in court, objects as well. Is the testimony admissible?