Emi's "Just another goodbye" is a speaker's raw reply to someone who is leaving. The opening answers a question we never hear, as if the other person has asked why this hurts so much. The speaker says they have already said goodbye too many times to count, and that the leaving person has now been reduced to one more in the pile. That label is meant to sting, and it also shows how worn down the speaker is.
The deeper wound is the broken promise. The goodbye was supposedly never going to happen, so even a simple "hello" now feels untrustworthy. The speaker is stuck between leaving cleanly and lingering in hope. The speaker also admits that people change and that a good opportunity is hard to turn down, which makes the hurt feel more resigned than angry.
The ending is the most striking part. After all this, the speaker begs the loved one never to come back, and the plea trails off into a lonely "Please." The mood is tired, tender and heartbroken, with a hint that returning would only reopen the wound.