Sometimes a person isn't aware of their real needs before entering a relationship. If you realize that you have different needs than the ones your current relationship provides, you should seriously consider breaking up.
Is the relationship badly affecting your life, career or well being? Then it's anything but a healthy one. When the relationship prevents you from growing or even worse, pulls you down, you should think about breaking up (See how to get over any person).
All couples fight but when fights become too frequent that they prevent you from enjoying your time then this might be an indication that you are not a good match for each other.
If guilt is the only thing that is preventing you from breaking up then you have to choose between living a sad life or breaking up.
When you become unable to do your hobbies, see your friends or live a good life, there is a very big possibility that you will experience tremendous dissatisfaction later on. Sometimes breaking up early is better than waiting for such a moment.
Do you break up every week or even every few days? Then sooner or later you will have to breakup for good. Take the decision now before you get more emotionally involved.
If you realize that you chose the wrong person under the effect of peer pressure, the fear of ending up alone or the desire to forget about an old relationship then know that sooner or later you will have to break up (See how to end loneliness).
If you always think about breaking up but are too afraid to break up because of fear, the inability to deal with the situation or embarrassment then know it's the right time to breakup.
Contrary to some beliefs, players usually don't change and had they believed that one person is enough they would have settled for them. When you realize you are with a player, break up immediately because sooner or later you will have to.
If the relationship is making you anything but happy then it's a strong sign that you should break up. If it's making you miserable then you don't need any further signs.
All couples fight and argue, but there are certain fights that point to a relationship being dysfunctional. If fights contain a large amount of insults and words said just for the sake of bringing someone down, then the relationship is probably not going to last and not supposed to last either.