All I can say is better to break up before the marriage than after. My parents divorced when I was very young, and although I am b’h happily married today, the scars of my childhood run deep, and the ache never goes away. That is the price of breaking up a marriage, and that is what you avoid if you don’t marry the person in the first place.
I have a close friend who noticed serious problems during her engagement but decided to go through with the wedding. She actually said, and I quote: “I would rather be married and divorced than not married at all”. Sure enough, she married the guy, got pregnant right away, the problems persisted, and they were divorced shortly after the baby was born, 1 month shy of their first anniversary. She says knowing what she knows now, she would have absolutely broken the engagement. She now finds herself in a very difficult situation: a single mother with limited shidduch prospects due to the divorce, the child, and the fact that kohanim are out.