I have had many difficult times with my current S.O. over 15+ years.

Everyone's situation is different, but I can say that in even a semi-healthy relationship, time heals many wounds, greater mutual understanding grows, hard edges can soften and people will often surprise you. You can also learn things you could improve about yourself which you were previously blind to. The sense of stability this reinforces is immensely helpful.

On the other hand, I also have an ex-- and while I wish I would have ended that differently in hindsight, it did need to end for my mental health to improve. If you are with someone who abuses you, cannot be reasoned with and never admits fault, it is wise to plan several exit strategies.