Love is compared to a flower here, and the comparison carries the whole poem. At first the speaker sounds gentle, calling love "pretty" and "calming." But the tone shifts at "But like every flower," when the poem turns to what love demands: effort. A flower left alone will die, and so will love if nobody looks after it.
The last three lines are the sharpest. The speaker stops describing and starts asking, almost challenging the reader: if you can't keep love alive, why think you deserve it? The final question, "Do you really deserve it?", is left hanging with no answer. It could be aimed at someone else, or the speaker may be questioning themselves. The poem doesn't say, and that uncertainty adds to the feeling.
The mood begins soft and peaceful, then becomes serious and a little uncomfortable. The plain, short lines make the warning feel direct, like a hard truth said quietly.