So it all started about 5 days ago, my best friend lets call her.. Jess and my other best friend lets call him... nick. Well Nick really likes jess he loves her. Me and nick text a lot, and he talks and talks and talks about her. I don't say anything because I don't want to be a bad friend. And I miss , us , who we were before he liked her and she knew. But Jess doesn't like nick , she does but as a friend. He wants to date her but she doesn't, I don't know what I should do from here he says she hurtsing him but he keeps going back

You do nothing-it's up to them how they live their lives.

Personally I'd be rather bored with a friend who could only discuss one subject-in this case 'Jess'.

You are supporting your friend (Nick) as any good friend would do. But it will get on your nerves if Nick goes on and on yapping about her.
You cant/dont-wanna do anything about what's going on between them because it's their problem, let them handle it.
But you should tell him that you have something in your mind. Tell him that it hurts (or you miss the "us") if he keeps on talking about her. He ought to know it, until you tell him, he won't even know what you are going through because right now, his whole mind is occupied with Jess

Don't be available to Nick when he talks/text about Jess. Say nothing of "US, they way we were" to Nick, matter of fact, you need less contact with him. He ain't thinking about "US", Jess ain't thinking about him, and you need to think about you, without him.