This is from the Surviving Infidelity board on Reddit and one of the most helpful pieces of advice I have read from u/Gusta-freda.
If you find yourself in a situation where your partner is unwilling to work for something so important to you, it feels like you are a victim. You are. I am. My husband never let on that something was wrong, that he was missing something. There were never any opportunities for me to help or to save our relationship. There are no words for how infuriating this is, however I will argue, I’m the lucky one. I have it easy. At the end of the day, even with all your shortcomings, you have not failed anybody. You just have to deal with the pain inflicted on you. The failure of the marriage is not on the person who was willing to work for it, but the person who decided all by themselves that no work will be done. This puts a lot of responsibility on that person. Don’t forget that in the process of destroying your life they have successfully destroyed their own lives as well. They might be completely sure they are doing the best thing for themselves and they will be happier. The thing is, they have to be right. If they are not (and they often aren’t), they have to face the destruction they caused for limited or no benefit. Research supports the idea that the grass rarely is greener. Don’t underestimate the guilt and the pressure plaguing that new relationship as well. You just have to take care of yourself. That is all. And you got this.