There are various theories concerning the dissolution of relationships. Firstly,
Lee argued that there are five stages involved in the process of a relationship coming to an end. The stages consist of dissatisfaction (one or both of the partners realise there are problems), exposure (the problems are brought out into the open), negotiation, resolution attempts and then finally termination, if the resolution attempts are unsuccessful. These stages were identified through a long term study of over 100 premarital romantic break-ups. He found that the strongest relationships tended to take the longest time to work through the five stages.
Duck's phase model isn't dissimilar to Lee's theory. He came up with four stages that are all triggered by a threshold. Firstly it is the intrapsychic phase where thoughts about negative aspects of the relationship or partner arise, but there is no discussion until the next phase, called the dyadic phase when the couple attempt to sort out their problems.
However these models focus on the sequence of likely events that lead to a break-up rather than focussing on the reasons behind the break down. Duck came up with internal and external explanations. The internal explanations are called predisposing personal factors which involves personal characteristics, which may change or you may becomes more aware of them, as well as interests and attitudes - for example if hobbies change you may spend less time with each other leading to the dissolution. During the initial phases of the relationship these factors might have been overlooked but may become progressively more significant.
Different backgrounds in terms of culture, race or religion give a relationship less stability. Also, young married couples are more likely to divorce as they tend to be less mature and haven't developed their adult personality so are more likely to change more.