Until you have resolved your Karma and fulfilled your Dharma, which are the deeds you must do, you will continue to reincarnate into sequential lifetime upon the earth. Neither God nor the Lords of Karma bestow suffering upon you during these lives, you and you alone decide what you most need to learn and in your earthly sojourns, and for each life experience you seek out other souls, often with shared histories, and always with Karmic configurations matching your needs. Whenever you act with intention you create Karma. Actions are considered to be thoughts, emotions, words and deeds, and the motive, desire and intent behind each. Disharmonious acts must be balanced in the future in this life or in a future lifetime, to have Soul growth.
In other words, if at the end of this lifetime, you have anything unresolved or incomplete you will have a chance to return in human form to correct those errors. Oftentimes our reincarnations are similar to past situations because the soul wishes to put the past to rest. The Universe is complicated, we all know that. Another way to think of it is, because it is so complicated, we need many lives to comprehend.