Relationships, be they romantic or not, can run their course and abruptly end. In some cases only one person really cared about the relationship. For them many questions will linger for many years. Their love will never fade. And when that chance encounter occurs they will be flooded with memories and questions. They are the ones who remember the smallest of details.
That relationship will never be repaired to where it once was. You can’t force someone to make you their priority. It’s either you are or you aren’t. The unanswered questions will remain just that. Hang on to the good memories and the rest is just fodder. It will not be of any benefit to you. Yes, this unexpected meeting was awkward, but you survived. Now keep moving.