Four short lines, and almost all of the feeling sits in the last one. The speaker begins by asking, "Don't you miss me?" It sounds like a real need to know, but then comes "Just asking," a quick, casual brush-off, as if the question didn't matter much. That small retreat is where the poem gets interesting. The speaker is trying to sound relaxed while clearly not being relaxed at all.
Then the mask slips. After the little pause of "cause," the speaker admits it plainly: "i miss you." The lowercase "i" makes the line feel even smaller and more private, like something typed late at night and almost left unsent. The mood is tender and a little vulnerable. The speaker wants reassurance but is too nervous to ask for it directly, so they offer their own feelings first and hope the other person will answer in kind. Nothing tells us who the "you" is, which lets many readers see themselves in it.