Is it wrong to daydream about sleeping with a married woman you have crush on?

Thoughts are one thing.
Actions are another.

I don't see the harm in it. I guess. Long as your keeping your hands to yourself.

Matthew 5:28 This is what Jesus has to say about it: But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart.

it’s not wrong, though i can’t imagine it’s very good for one in the long run.

There is nothing wrong with daydreaming as long as it does not become an obsession.

It's just thoughts not actions those are what matter

Contrary to what the nuns told us, thoughts are not actions. As long as they stay daydreams you're not doing any harm.

If so, I've been wrong before

Of course