"I'll come to thee by moonlight, though hell should bar the way." (line 30)
This is a pretty brave thing to say, and it shows the highwayman's fearless devotion to Bess. Well, at least he claims to be fearless. We don't have any way to be sure yet. As the poem goes on, we learn that he really is a pretty brave guy (maybe a little too brave) and definitely as good as his word. In fact a highway robber without any courage probably wouldn't last long. Not a great career choice for cowards.
She writhed her hands till her fingers were wet with sweat or blood. (line 56)
Bess is pretty brave too. Some heroines would just cry and wait to be rescued. Not Bess. She makes a plan and she follows through. We can almost feel the tight, sharp pain in her hands here, but that's not enough to make her give up. Her real moment of bravery is still to come, but her quick thinking and her toughness in this moment say a lot about her character.
Her eyes grew wide for a moment; she drew one last deep breath, (line 75)
This is the big moment. The speaker pauses along with her, waits while she prepares herself to do the unthinkable. This is the moment when you really need courage, when you're facing death. And yet…something isn't quite right here. We generally like courageous people, and people who will do anything for love but isn't this taking it a little far? Are we really supposed to admire Bess for committing suicide?