In order to save your marriage you will have to make sure that it is what both you and your partner want to happen. If your partner isn't interested in trying to save your marriage anymore, then maybe it is not worth saving.
If the situation has gotten so serious that one partner is getting ready to leave then perhaps there is no real need to try. Maybe there isn't anything that can be done even though one of you may be thinking--"I want to save my marriage."
Before your relationship does go this far, maybe you should each take responsibility for actions which lead to the downward spiral in your marriage. Get together and discuss what each other expects from the marriage and what needs have not yet been met. While discussing the relationship neither partner should try to blame the other for what has already gone wrong. Each partner in this relationship should be willing to take responsibility for their contribution to the failure of the relationship and begin to mend fences from that point on.
After you have had time to figure out where things stand, try to communicate with each other instead of arguing. Be open minded and try to work as a team for the same goal. Find a middle ground where you both can feel safe and at ease discussing the matter truthfully. Try to be cooperative with each other in finding a resolution to your problems.
If I were wondering how I could save my marriage, I would be serious enough to realize that I have to take blame for my own fault in what has happened. Until each partner is able to get to this point, there is no moving on. Be rational and reasonable because blaming each other can only worsen the situation.
Don't go through marriage arguing each day and still not realizing that something serious is going on with your relationship. Don't be in denial thinking, "My marriage doesn't need to be saved because it's not in any danger." Denial will not get you very far in your relationship. The problems will just get deeper and in more danger of ending your marriage.
Just because you have gotten married doesn't mean that you and your spouse have to give up your own way of thinking. You had your own opinions about certain things before you were married and this fact will still be true after you are married. This doesn't mean you are incompatible. There is almost always a middle ground and you can work with each other instead of one person trying to change the other. Just leave the line of communication open, always, and you may be able to save your marriage.