The most common and most likely answer to this crossword clue is the 7 letter word SORRIER
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More clues leading to the result SORRIER
Buddy explains!

The straight part
We know that "More regretful" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case more regretful = sorrier.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SORRIER mean?
SORRIER adjective- (of a person) Regretful for an action; grieved or saddened, especially by the loss of something or someone.
- Poor, pitifully sad or regrettable.
- Pathetic and inferior to the point of causing others disgust.