I saw this from somewhere "一個人很空虛，兩個人太委屈".
In English, it means "When you are alone, you feel empty. But when you are with him/her, both of you suffered grievously."
Sometimes, you might come to a crossroad for love, when it calls for you to make a choice. To stay and continue to make each other's life miserable, but at the very least you have a "somebody" or to pack up and go, leaving all the unhappiness behind and dive into the uncertainties ahead of you?
I had in the past, tried staying for one and leaving for the other and my verdict was - It's wiser to leave... than to be left!
Of course, staying has its advantage, because who knows, your problem might be resolved, your partner might 'turn over a new leaf', your endurance might pay off and the two of you might love each other forever.
But personally, I would still favor the choice of leaving. Life is just too short to live each day blaming your partner.