May I attend a close friend’s interfaith wedding if I know know that skipping it would push him further away from Judaism?
In general, we do not attend a wedding when the person is intermarrying. Attending the wedding is in a way giving credence to the abomination that this person is doing, and encouraging him in his sin. A person who is intermarrying is turning his back and future to Judaism, and at this point has no interest in it. In order to make an exception, I would need to know the specific circumstances why things should be different here.