Two short lines, and almost nothing happens in them. A speaker admits that someone is still on their mind, and that it happens more often than they'd like. That's the whole confession, but the way it's put says a lot.
Notice the words "I guess." The speaker sounds casual, almost shrugging, as if trying to keep this light. But the second line gives them away. Nobody says "more than I would like to admit" about a passing thought. It suggests the feeling is bigger than they want it to be, and a little embarrassing to own up to. The word "still" matters too: it hints that time has passed and the speaker expected to have moved on by now.
The mood is quiet, wistful and slightly sheepish. There's no drama or blame, just an honest, low-key moment of vulnerability. The brevity helps: the speaker says as little as possible, yet can't quite hide how much they feel. We never learn who "you" is, so readers can fill in their own someone.