Mark writes to Juliet. His tone is exasperated as he insists that, as Juliet requested, he's given her time and not mentioned marriage. However, he takes great offense to her going to Guernsey and calls her ridiculous. He lists all the ways that she makes him happy and accuses her of running away. In closing, he offers to take her to Guernsey on their honeymoon if he has to.
Notice that Mark doesn't say or ask anything about how Juliet might feel; his self-centeredness again shows that he doesn't value Juliet, her friends, or her independence. By continuing to call her names, he sets up that the only way to make the abuse stop is to marry him.
Juliet writes back and says she's going to Guernsey and still can't give Mark an answer. He offers to drive her to meet the boat and she accepts, though she asks that he not lecture her.
Accepting Mark's offer shows that Juliet still wonders if turning him down is the right thing, given how "perfect" he is.