This is the huge dilemma that Ethan must deal with and somehow try to resolve. He's stuck in a loveless marriage to Zenobia, or Zeena, a marriage in which he feels increasingly isolated and alone. At the same time, he feels duty-bound to stay with Zeena, even though it's causing him such deep unhappiness. Under the circumstances, it's no wonder that Ethan tries to escape his dilemma by attempting suicide. As it happens, however, this isn't a way of dealing with his problems but rather his way of running away from them. His suicide attempt, far from liberating him from Zeena, actually makes him more dependent on her due to the injuries he sustained.
One could argue that getting a divorce would've been the right thing to do for Ethan; at least he could've moved on with his life. But it's not quite as simple as that. In those days, divorce was frowned upon by society, and Ethan doesn't want to have to deal with the scandal that would ensue were he to take the fateful step of breaking-up with Zeena. So he remains trapped.
In Ethan's unenviable situation we can observe Wharton's powerful critique of the social mores of her time that kept so many people in a perpetual state of unhappiness.