Listen to Marina say, "I can't watch you die! I love you."
Heck, before that, she is begging him to run away. She doesn't want him or Proteus or anyone else to die. She starts the first part of the five stages of grief before breaking down in tears.
Sinbad's acting like a total asshole to Marina after she (along with Spike) saved him and the entire crew. Her frustration is easy to understand, as well as a silent What the Hell, Hero? look from his crew.
A minor scene, but Dymas tries to convince his son to escape from Syracuse before the day of his execution comes, only to obtain a refusal. While Proteus's trust in Sinbad is not misplaced, it did not appear so at the time, so his father clearly expects to see him die for nothing.
Sinbad's farewell to his mates when they reach their destination.
He leaves his ship to Kale and affectionately tells Spike he can't come along.
Sinbad returning to take Proteus' place when he couldn't get back the Book of Peace. He's absolutely terrified, but he doesn't run or try to talk his way out of it. Even though Eris came in time, at that moment, he was prepared to die.
The look on Proteus' face when Sinbad admits that he doesn't have the book. The Little "No" he gives along with it just cements it.
Spike wanting to stop the execution, only for Marina to hold him back.
