Is expiation obligatory for someone who said, "By Allah, he will not come," out of despair over the arrival of a person, after he had promised to visit at a specific time and was delayed?

If a person swears an oath concerning a future matter based on what they predominantly believe to be true, and then it turns out to be otherwise, there is no expiation (kaffarah) upon them, nor is there sin. This is the choice of Shaykh al-Islam Ibn Taymiyyah, because they are considered truthful in their oath, having sworn based on what they believed. An example of this is if someone swears that a person will arrive, believing it to be true, and then that person does not come.