Someone is replaying a situation they can't let go of. The speaker never says what went wrong, and that vagueness is part of what makes the poem feel real. Something happened, or something ended, and now the mind won't rest. "My mind keeps racing" captures that restless, spinning feeling when you lie awake going over the same moments again and again.
The two questions, set apart from the rest of the lines, stand out like thoughts that keep interrupting. "What was the problem?" looks for a cause, and "Could it have been fixed?" looks for blame or regret. Neither gets an answer. The speaker admits "there's no explaining" and accepts that they'll "just go on wondering," and the trailing dots suggest the thinking doesn't really stop.
The mood is quiet, anxious, and a little tired. There's no anger or drama here, only the sadness of not having closure and the sense of being stuck with unanswered what-ifs.