Should one grieve over the loss of money that would have been spent on the sin of adultery, or rejoice that Allah has saved him from falling into it?

The harm of losing money cannot be compared to the harm of losing one's religion. Therefore, praise Allah for diverting you from adultery, which is one of the major sins. Allah Almighty said: "And do not approach unlawful sexual intercourse. Indeed, it is ever an immorality and is evil as a way." And Allah Almighty said: "And those who do not invoke with Allah another deity or kill the soul which Allah has forbidden [to be killed], except by right, and do not commit unlawful sexual intercourse. And whoever does that will meet a penalty. Multiplied for him will be the punishment on the Day of Resurrection, and he will abide therein humiliated – Except for those who repent, believe and do righteous deeds; for them Allah will change their evil deeds into good ones. And ever is Allah Forgiving and Merciful." You must offer sincere repentance for your intention to commit this immoral act and take the necessary measures to help you safeguard yourself from what is unlawful.