Possible Clues:

• Failing tic-tac-toe row
• Unhelpful noughts-and-crosses line
• Cat's game row
• Losing row in tic-tac-toe
• Letters on a love letter
• Intimate email sign-off
• Losing tic-tac-toe combo
• Kiss and hugs, in a love letter
• Failed line in tic-tac-toe