Islam teaches the believers to turn to Allah consistently for guidance, succor, grace and mercy in each and every problem they face in life. 

By consistently turning to Allah, one empowers himself/herself and thus becomes invigorated and strengthened spiritually and morally. 

Istikharah has been prescribed as a method of seeking Allah’s help whenever we find ourselves unable to make up our mind between two equally valid options both of which are considered halal(permissible). 

It must, however, be clearly borne in mind that istikharah does not apply to choosing between options, one or both of which are considered haram (unlawful), since there is no question of choice in haram, as we must always shun it. 

According to an authentic report, the Prophet (peace and blessings be upon him) used to teach his Companions the prayer of istikharah even as he used to teach them surahs (chapters) of the Qur’an. This shows the great significance of istikharah. 

While stressing the great value of istikharah, it is important to point out that it should not be considered as a substitute for doing what is required of us to do Islamically. In other words, while doing istikharah or even before doing it — especially in cases such as the one mentioned in your question — one must do all that is possible to make one’s marriage work. 

You must exhaust all the means and efforts at your disposal by taking all of the necessary steps to reconcile your differences. To be able to do this most efficiently, you must seek proper Islamic guidance and counseling. 

Besides, you must take personal responsibility in consciously changing your attitude and behavior by asking the following questions: 

1. Are there things I am doing that cause or aggravate my marriage problems? 

2. Are there things I can do on a regular basis in order to elicit kind and loving responses from my spouse? 

3. Am I dwelling too often on what we don’t have rather than focusing on the blessings we readily possess? Most probably, one of the root causes of all of our miseries in life as well as in marriage is our dwelling on the negatives and our failure to thank Allah for His favors. 

4. Have I been focusing too much on the negative aspects of my spouse? Can I try shifting my focus to dwell on my own weaknesses and the strengths of my spouse? 

By consistently taking practical steps to change our attitudes and seeking Allah’s help in improving ourselves through istikharah and otherwise, we can find proper Islamic solutions to our problems.“Surely Allah is with those who are consistently doing what is good.” (?An-Nahl: 128)" 

http://www.onislam.net/english/ask-the-scholar/acts-of-worship/prayer/supererogatory-prayers/169405.html

https://www.islamstory.com/en/artical/25084/istikharah-end-marriage-ok?