I beat it but kind of raced through it a little and didn't really get the full story of it. What was Ulysses goal and how does involve the player (courier)??

I think he wanted revenge. Leading the Courier to their death with the pomise of answers.
The Courier once delivered a package containing a detonator. This detonator activated the nukes below the Divide, a settlement that Ulysses saw a vast amount of potential in. Ulysses was the Legion frumentarius who discovered Hoover Dam, thus leading the Legion to the Mojave, and the original Courier Six. He dropped out when he saw your name was next on the list, hoping the mojave would kill you. In the end of the DLC, I'm not sure why he fired the nukes, but the Marked Men are alerted and come running to attack. Ulysses did this as a last-ditch effort to ensure that if he could not kill you, they would. Although you can convince him that he's a hypocrite, doing exactly what he accuses you of doing