A friend of mine said to me, if she sees any potential possibility of a breakup, she would never go into a relationship. For example, a habit, behavior, lifestyle that she doesn't like about the guy. This avoids wasting youth and heartbreak. Yes, you may find that she would have lost the love of her lifetime but it is a choice she made. And it also makes sense, when you feel some feelings going on, you should put some rational logic in place to counter fight off any fling and lure. You don't want to fall in and then start hurting yourself to overcome something you hate and thinking that your love will give up a habit for you. The saying, a leopard will not change its spots, and a zebra will not change its stripes.
Preventing yourself from getting in a wrong relationship is the first line of defense one should have. Go through his/her good and bad, is that something you can accept, compromise, and put down. Go through it in your mind and see if you can live with it. If she smokes, imagine yourself with her meeting your friends, relatives, or parent and after a while or meal, she went for a smoke. Can you accept that? It wouldn't be a problem if you smoke too. :-). But you get my point what I mean here. Or she is divorced and you should prepare that she is more sensitive in a relationship and it means some hardship in getting her trust that your love for her.
I would suggest writing down the list and if you decide to go fore with the relationship, use that as a reminder, never use that as an excuse to break it off as you had already considered it. And if you had used it for an excuse, re-think, it may be something else that had trigger the thoughts to use that against yourself. We all know that when one in love, things get complicated, two-person coming together, different backgrounds, cultures, lifestyles, and families do play a part. The world is changing by the minute, Circumstances changes, and people change. A bad-tempered man would change to a calm loving and thoughtful father in front of his little girl.
Still, it all up to you to make the choice, there is no right or wrong. It depends on how you want to move on from there. Look at the list when you are in doubt, remind yourself of your initial decision, and if you have already considered the possibility and the relationship still did not work out? Maybe it is time to let go, be rational as you have already tried your best. Have a good sob, a good dessert always help, list activities for the next few days, something out of your comfort zone, new excitement will push you to relieve your thoughts and hurt from a failed relationship. Feel like shouting it out? Have you tried karaoke? That's one of the good ways, a few sad songs and move to some fast pace songs to feel the mood that you can face the new world again.
Someone I know is more down to earth, he starts calling his group of school mates for a meetup after a long journey failed relationship, end up heading out tour with a few closer one and catch up with his old friends got over his relationship.
I hope this helps a little if you are still trying to figure if you should be in or out of a relationship. When the heart can't make the decision, let the brain work rationally and decide for yourself.
No one can make that decision for you. Only yourself.