Three short lines carry a surprisingly big idea: the speaker fell for someone because that person loved them first, at a time when they couldn't manage to love themselves. The love here isn't described as sparkling or dramatic. It's described as a kind of rescue. Someone else saw something worth loving when the speaker saw nothing.
The speaker's feeling is mostly gratitude, mixed with a quiet vulnerability. Admitting "I couldn't love myself" is an honest, exposed thing to say, and the poem doesn't dress it up. The opening line, "I feel in love," looks like a slip for "fell," though it also accidentally suggests the speaker is feeling this love now, in the present. The mood is tender, plain, and a little sad, because the pain of self-doubt sits right beside the warmth. The brevity makes it feel like a confession, said simply and without defense.