Written as a single line, "realisation" admits something that feels almost too big for one sentence: the speaker holds extreme joy and extreme sadness at the same time. They don't say they swing between the two or that one follows the other. They say they are *both*, and that you will never meet anyone who is more of either.
The title matters here. A realisation is a moment of seeing something clearly, so the line reads less like a complaint and more like a discovery. The speaker seems to have noticed that these feelings aren't opposites that cancel out. They live side by side.
The mood is quiet, honest and a little unsettled. The direct "you" makes it feel like a confession made to a stranger, and the short length leaves a lot unsaid. We never learn why the speaker feels this way, which lets many readers recognise their own mixed feelings in it.