There is a saying that there is no such thing as halfway pregnant.  From the Halakhic perspective, there is no such thing as halfway married.  Our Gemara on amud aleph tells us:

אִילּוּ אָמַר לְאִשָּׁה ״הַיּוֹם אַתְּ אִשְׁתִּי וּלְמָחָר אִי אַתְּ אִשְׁתִּי״, מִי נָפְקָא בְּלָא גֵּט?!

And what would happen if one said to a woman while performing betrothal: Today you are my wife and tomorrow you are not my wife? Would she exit the marriage the next day without a bill of divorce?  Of course not, as her marriage once activated, is complete. 

This is not only true halakhically, but it is true psychologically.  A good marriage cannot exist when one partner or the other has their foot out the door.  To make a relationship work requires full commitment.  Otherwise, every flaw will be magnified and every asset minimized.  However, if you commit to a relationship, your natural wish for success and self preservation, even a purchaser’s bias, takes effect and you can see the good.  Is this false?  How do you decide what is false?  Some say, the difference between a pessimist and an optimist is how they evaluate the same events. The truth is hard to come by, but how we feel about matters affects how we, so to speak, feel.  And how we feel arguably is often more important for our health and well being than objective facts.

But, what do you do when you really are ambivalent and are unsure if you should stay married to this person?  To deny reality is like refusing to sell a bad investment and watching it tank.  Sometimes, it's better to cut your losses.  This is true, but how do you know if it is true in your situation?  

A good approach is to set bounds for the problem.  Write a letter to your future self, delineating what you would need to see change, as a bare minimum, to think that the relationship has potential.  Seal it and resolve to not open it for six months, or send yourself an email with “schedule send option.”  Then, forget about the letter and throw yourself into the relationship full speed.  When it comes time to open the letter you will now have had a significant period of time, with positive engagement and optimism, to see if there was notable improvement.  Having this promise to yourself will give you the emotional safety to give it your all without fear of losing yourself.