regretful (adj.)

• apologetic
• ashamed
• baffled
• blasted
• blighted
• chapfallen
• conscience-smitten
• contrite
• crestfallen
• crossed
• crushed
• dashed
• defeated
• disappointed
• dished
• disillusioned
• dissatisfied
• foiled
• frustrated
• guilty
• mournful
• penitent
• remorseful
• repentant
• rueful
• sad
• shamefaced
• shameful
• sorrowful
• sorry
• soured
• thwarted
• wistful