There are things we do to each other in a marriage that are devastating. Infidelity, secrets and lies, abuse. Coming out on top after situations like these is incredibly challenging. It takes two people who are very committed to making things work, who've prayed about it and asked God for continued support, and above all else, are willing to let the past go to move on to the future.
All too often, we can really hold on to hurt and allow it to consume our lives. For some, it's challenging but not impossible to let the hurt go, but for the majority, the hurt lingers for months and even years.
If there are still unresolved circumstances in your marriage, the past can never be let go. Consider joining a marriage healing group or attending a marriage conference to learn new ways of replacing the hurt with joy. In fact, that is probably one of the best things you can do. Knowing that you are not alone in your hurt and other people are in your same situation can be cathardic in its' own right. More so than anything, if you keep trying to "fix" the problem on your own without the right tools, you could still be taking damaging action that can hinder your progress in the right direction.
There are some circumstances in the Bible where divorce is an option, I will let you research that yourself, because I think it should be the ultimate last resort. However, if you are continually being abused or if your spouse is continuing to engage in intimate relationships with other people, these are things that might not be able to be fixed. But if you are both committed, you can get over these things with the help of God and other supporters in your life. Take heart, the past doesn't have to continue on in your future. Not only that, God uses our past to help others with their futures. You never know when God might call you to say, write a marriage Bible study someday or speak and counsel to other married couples because you've been able to overcome the past together.