Destiny, sometimes referred to as fate (from Latin fatum – destiny), is a predetermined course of events. It may be conceived as a predetermined future, whether in general or of an individual.
Allah (SWT) knows the fate of everyone after death. We are responsible to seek true knowledge about the message of Islam and follow it. Everyone will be asked in the Day of Judgement about his faith and practice. Muslims will be questioned whether they obeyed the Prophetic orders or not. Prophet Muhammad (SAWA) ordered all Muslims to keep following Quran and Ahlul Bayt (AS). This is in the authentic known as Hadeeth al-Thaqalain which is narrated in main Sunni and Shia books of Hadeeth e.g. (Saheeh Muslim, Hadeeth number 4425, Tirmithi; 3718, Musnad Ahmad ibn Hanbal ; 10681, Al-Mustadrak by Al-Nisabouri; 4576, Al-Sunan al-Khubra by Al-Nasaa'ee; 6921 and many other Sunni books.
Those who did not care to search for the truth will be questioned and those who knew but did not follow will face the result of their ignoring the orders of the Prophet (SAWA).
We believe that all Muslims who sincerely believe in Allah and the Messenger will ultimately go to Paradise even after they had to face results of their mistakes.This applies on followers of all Muslim sects except the enemies of Ahlul Bayt (AS).
It is really difficult for us human beings to know what aspects of fate are unchangeable and which are changeable as this knowledge belongs to Allah. However, hadith say that some unwanted things which are fated can be changed by prayer (du'a) or good acts (such as charity). God knows best.
Here are some thoughts on that: https://www.al-islam.org/ask/can-dua-change-your-taqdeer-and-fate
Thank you for your question. For many issues of fate and free will, it is useful to see the circumstances as fate and the choices we make as being of our own volition. That is that we cannot control the time we are born in, the circumstances we are brought up in, the country we live in, and so on, and as such the person we marry will be connected to these circumstances in some way and we cannot control that. On the other hand, the choice of who we marry is our own, even if God has pre-eternal knowledge of that choice, and has put us in the best situation. It is important for us to truly make choices for ourselves as that is what meaningful free will is.
As for the verses speaking about the humans being created in pairs, this is to do with the human race as a whole (i.e there being males and females) rather than as soul mates. As you are aware Islam allows for polygyny as well as multiple temporary and permanent marriages depending on which marriages work out and for what purpose they are contracted. The concept of soul mates is somewhat alien to the Islamic perspective on marriage as far as I am aware.
May you always be successful
Yes, of course.
It is narrated that the Prophet (S) said, "Nothing wards off fate except supplication."
It is narrated that Imam al-Kazim (A) said, "I urge you to supplicate, for verily supplication to Allah and seeking from Allah repels calamity which may have been destined and decreed with just the execution remaining, so if Allah is supplicated and is asked to avert a calamity, it is averted."
The Qur'an also strongly encourages us to call to God and seek what we want or need from Him.
Also, certain acts, such as giving charity, can change aspects of our fate that have been decreed.
Of course, sometimes Allah does not grant our requests, out of His wisdom or as part of a greater plan.
There are some things in our fate that are fixed and unchangeable, and some things that are changeable; we don't know which are which, so we can do du'a regarding all of them, and leave the response to Allah.