How we cite our quotes: (Line)
Quote #1
The broken sheds look'd sad and strange: (5)
The speaker finds all of the landscape sad. Or is that because he's setting the scene for Mariana's sadness? Either way, it isn't just our main character that is full of sorrow. Every image in the poem enforces a gloomy, dreary disposition. This is just the only time he really tells us what an inanimate object actually feels.
Quote #2
She only said, "My life is dreary,
He cometh not," she said; (9-10)
This is the first time we understand the cause of Mariana's sorrows: a man who has not returned to her. Even without the epigraph—which ties her to the character in Measure for Measure who has been jilted and so decides to live in seclusion—we can see that it's been some time since he's been around. Her sadness, then, has been brewing. Still, she seems hopeful that someday he will return.
Quote #3
She could not look on the sweet heaven,
Either at morn or eventide. (15-16)
She's so sad that she can't even look up into the sky. "Heaven" is usually a place that people look forward to, but Tennyson is saying that she feels like she has nothing at all to look forward to. If there's anything good around her, she isn't going to notice it. Mariana is fully stuck within her mind, and can think only of her own sorrow.