Such a decision is for you and you alone but how do you come to a decision that allows you to have peace in such a life changing process?
There is no hard and fast rules. However, some of us with major relationship issues tend to allow, as an example, abuse to continue one and on and we do not act on it, we weather it. Or our partner has an affair and we forgive him/her, which is your right, then it happens again and again. Some people will allow it to go on- as the alternative- separation is worse to bare. Where is the benchmark to take action?
Often people in such distress seek other peoples opinions by telling them in confidence what they are putting up with. This disclosure will receive opinion based on what that person believe sis what "they would do" in a similar situation. But is it unbiased? A girlfriend of a lady in a abusive relationship might well be biased especially if she doesnt like her friends husband, a single man best mates with a husband that is married to a woman that is having affairs can paint a rosy life as a single guy and so on. My point being - confiding in friends is ok for company, for a general opinion, but it is not necessarily a fine way to base any action on. It is comforting only and that is the extent of the benefit.
The next step is professional comfort by means of relationship counseling. This step can be daunting at first and disappointing that you have resorted to "help". This first step should include an invitation to your spouse to join you in "fine tuning" your relationship (rather than - "we need help to save our marriage"). This request can be met with a "no" response. What now? How can you mend a broken marriage without counseling together? What you do is go to counseling yourself. But there should be one condition to yourself- if your spouse does not wan tto attend counseling then there is not privilege to the details of such counseling. If he'she asks what happened the answer can be "Well you chose not to come so if you want to help me out can you come next time". If you then disclose what was said at you previous meetings then you risk your spouse pulling out of going altogether as it might seem he wont be given a fair hearing.
Every potential relationship split is unique in circumstances, install your own boundaries of behaviour, trust yourself in what you want in life and introduce counseling. Be fair, firm, reasonable, realistic, flexible, determined and self protective. Then make your decision.