There should be only one reason - because you have tried every reasonable route to compromise and you cannot stand living with your spouse any longer.
In the end the consideration as to whether you can sacrifice your own life for the sake of others, for money, for penance for misdeeds in a past life, for a reward in a future life, for fear of failure or change, for your career, for money, for the dog will be outweighed by your need to escape your current situation and only then should you consult a divorce lawyer.
The answer to the question - How do you know when you are in love? - is -
The answer to the question - How do you know if you should get divorced ? - is the same.