Why is my cavi all of a sudden not wanting to go for long walks?

There could be several reasons why your cavi (assuming you mean Cavalier King Charles Spaniel) is not wanting to go for long walks. It could be due to age-related joint pain or Arthritis, underlying health issues, fatigue, anxiety, or simply a change in their preferences or routine. It's important to observe any other accompanying symptoms, consult with a veterinarian for a thorough examination, and consider adjusting their exercise regimen accordingly.