Is constant fear of breaking off the engagement, along with the fiances' commitment to prayer and encouraging each other in it, and a feeling of strange energy after their meetings, normal during an engagement period that may extend for four years?

There is no justification for feeling afraid of breaking off an engagement, and overthinking it is a mistake, because what Allah has decreed will come to pass. Everything that happens in this world is by Allah's decree, written fifty thousand years before the creation of the world, and in it there is mercy and wisdom. Therefore, one must have a good opinion of Allah and entrust all matters to Him. A believer does not attach their heart to anything of this world, knowing that it is transient. The Prophet, peace and blessings be upon him, said: "Live as long as you wish, for you shall die; love whom you wish, for you shall part; and do what you wish, for you shall be recompensed for it." It must be noted that a suitor is a stranger to his fiancée before the legal contract, so it is not permissible for him to be alone with her or to engage in extensive conversation with her without need.