I really do think that some people believe things will get better, even if the chance is slim to none, they want to be that 1% that makes it through with a rainbow at the end...
If the relationship is really unhealthy, chances are that even if anything does get better, there is still likely to be issues that will be difficult to deal with and live with.
There's no coping - just accepting it for whatever reasons. But to me, that's not a true relationship. That's extended sorrow...
I believe there are definitely things that we will learn from everyone who crosses our paths, whether it be positive or negative. We all know no one's perfect but watering dead grass wont revive it. You have to decide for yourself what you're willing to accept and what you won't. *And if there are children involved, the children's safety needs to be priority (physically and mentally.)*
This is why it's so important to have the Lord, to seek to build a relationship with the Lord - He'll guide you in all that you do and you'll know what the right decisions are.
One thing is certain: LOVE SHOULD NOT HURT.
God bless :)