Jealousy: why asking them again only helps for an hour
The reassurance is real and it never lasts. Questioning your partner is a compulsion, and withdrawing it, kindly and by agreement, is one of the most effective parts of treatment.

You ask. Where were you, who was there, why did it take so long. They answer, and the answer is plausible, and for a while it holds. Then the doubt finds a gap. But they said the meeting ended at six and the message came at half past. And you ask again, in a different way, and you can hear yourself, and you hate it, and you cannot stop.
Questioning is the compulsion in pathological jealousy that involves another person most directly, and it is usually the one doing the most damage to the relationship. I want to explain why it fails, and how it gets withdrawn.
What reassurance does
Reassurance works, briefly. That is the whole problem. The answer arrives, the anxiety drops, and the drop is a reward. Your brain learns: asking helped, ask again. At the same time it learns something else: that the doubt was serious enough to need checking. So the next doubt comes in louder, and needs a bigger answer, and the answer holds for less time.
This is exactly what happens with reassurance in every form of OCD. The person with contamination fears who asks "is this clean?" feels better for a minute. The person with harm thoughts who asks "you know I'd never do that, right?" feels better for an hour. The relief is real, and it is the fuel.
Why it gets worse for both of you
There is a second cost. Over time the relationship reorganises itself around the reassurance. Your partner becomes an answering machine. They learn to pre-empt the questions, to account for their time before being asked, to avoid mentioning certain names. Some of that is kindness. All of it is exhausting, and the resentment builds on both sides: theirs at being interrogated, yours at needing to.
And the accounting itself becomes suspicious. Why are they explaining so carefully? What are they covering? The reassurance that was meant to settle the doubt becomes new material for it.
Withdrawing it
The obvious move is to stop asking, and the obvious move fails, because the urge peaks and the question comes out anyway, and the failure gets filed as evidence that you cannot control it. Reassurance withdrawn abruptly, whether by you or by your partner, also feels like a punishment and usually backfires.
So in the CBT work we do it gradually, agreed in advance, and with warmth. The steps are yours to set. Perhaps the first is not asking a follow-up question. Then not asking about a particular kind of evening. Then letting the message go unexamined. At each step, the doubt rises, and you find out what happens when it is not answered: it falls, on its own, and you get through the evening.
Explaining the plan to your partner
This is individual therapy rather than couples work, but it often helps to explain the plan to your partner so the reassurance can be withdrawn kindly rather than as a punishment. A partner who knows what is happening can decline warmly: "We agreed I wouldn't answer that one. I'm here, and I'm not going to go through the timeline." A partner who does not know will seem to be hiding something, and the silence becomes evidence.
Some people bring their partner to a single session for exactly this conversation. That is fine if you both want it, and it is often the session that changes the tone at home.
What I will not say
I will not tell you your partner is trustworthy. I do not know, and it would be one more reassurance to wear off by morning. What I can help you build is the ability to get through the day without needing certainty, which is what everyone in a relationship does, whether they notice it or not.
If asking has become the thing you cannot stop, there is more on how I treat pathological jealousy, and withdrawing the questions is one of the first steps we plan.