Two short lines carry all the feeling here. The speaker looks at someone else and wishes that person cared about them as much as they themselves care. The poem never says it outright, but the word "that" gives it away: the speaker has a clear sense of how much love or attention is being shown, and they know it falls short of what they're giving, or what they need.
The tone is quiet and sad rather than angry. "Oh how I wish" sounds like a sigh, a little helpless, as if the speaker has already accepted that wishing is all they can do. There's no blame or accusation, just longing. The brevity helps. With so few words, the poem feels like a thought spoken under the breath, something the speaker may never say to the person's face. The mood is one of unreturned affection, a small, honest ache that many readers will recognize.