Two short lines carry a surprisingly big contradiction. The speaker is talking directly to someone, and admits to feeling love and hatred toward that person at the same time, both stronger than ever before. The poem doesn't say why. We get no story about a betrayal or a breakup, so the feeling itself is what we are left with.
The grammar is worth noticing. "I've never loved and hated you this much" treats the two emotions as a pair, almost as one feeling with two faces. The speaker doesn't choose between them or try to sort them out. That suggests the hatred isn't the opposite of love here; it may grow from the same source, since you can only be this angry at someone who matters this much.
The mood is raw and breathless. With so few words and no decoration, the poem feels like something blurted out in a heated moment, honest and a little helpless, with nothing left to say after it.