The future is the time after the present. Its arrival is considered inevitable due to the existence of time and the laws of physics. Due to the apparent nature of reality and the unavoidability of the future, everything that currently exists and will exist can be categorized as either permanent, meaning that it will exist forever, or temporary, meaning that it will end.
The goal of istikhara, as presented in hadith, is to seek divine wisdom for what path we should take. So, from that angle, the goal of istikhara is not to see how someone's character will be in a marriage.
However, some scholars who have a lot of experience performing istikharas might sometimes be able to offer some insights on the matter, especially if it is glaringly apparent.
I will not lecture you about God's comparison and mercy, as you must be well aware of how the Almighty forgives all sins, and cleans our slates once we turn to Him with sincere repentance.
It is forgetting the past that you must be focusing on, and how you are able to develop a level of piety that you will enter into a new phase in your life, based on religious devotion and spiritual growth. That will not just ensure you've been forgiven, but also keep you on the straight path.
Your sin is between you and Allah ta'ala, and you must not reveal it to anybody. From a shar'i perspective, you do not need to tell your future spouse your previous sin.
Once you have changed your ways and sincerely forgiven, and became more religiously active and aware, then you live your life normally, and think positively for the future, not allowing the past to define who you are.
With prayers for your success.
Just because you prayed to ask that someone not being involved in your life or around you anymore does not mean they will have to disappear, or that it will mean something or be a sign for something.
You must try to live your life, and not allow yourself to be concerned or emotionally investing yourself in another individual who might/might not even be interested in you.
It is for you to do dua that Allah ta'ala grants you a noble, righteous and loyal spouse, whoever that may be, and leave the rest for the Almighty.
With prayers for your success.
No one is allowed to claim any matter in the meanings of Quran with out authentic evidence from the Prophet (SAWA) or Ahlul Bayt (AS). There are authentic Hadeeths from the Prophet (SAWA) cursing any one who does that.
The scholars who know approximate meanings of Quran some times take Estikhara from Quran, but this is allowed only for those who have enough knowledge about Quranic verses meanings.
as salam alaikum
there is no precedence of such practice in the sirah of the Prophet and the Ahl al-Bayt, peace be upon them. It is also reported on the authority of Imam al-Sadiq, peace be upon him: "Do not predict future events by the Qur'an" (al-Kafi, vol. 2, p.629).
With prayers for your success.
This is a complicated question, not the least because many things can happen that we don't expect. No one in the 1800s could have expected the world today!
Islam in today's world is heavily interwoven with the social and political challenges and changes of the past century, especially regarding Westernization, the framework of modernity (secularism, the nation-state system, etc), and changes in technology. For instance, "Islam" and "the West" are often treated as antonyms.
In the coming centuries, I think that (a) the power center of the world will shift away from Western countries, probably to somewhere in Asia; therefore, "Islam and the West" will no longer be a defining issue. Often, today, identity is a heavy part of Islamic discourse (for instance, hijab as the "flag of Islam"), and I think this will lessen as cultural and economic power shifts to other regions.
Also, in the past century, many Muslims have reframed their approach to Islam in light of paradigms that are part of modernity (such as science as a modern-day replacement for religion, promoting political systems such as communism or democracy, technology as the savior, Islam as "modern", the worship of progress). The world is starting to see that modernity (technologcal or ideological) isn't the savior that it was once thought to be and has in fact brought a lot of harm and suffering along with good, but I feel that sometimes Islamic discourse is a bit slow to move on from these things. In fact some Muslims are still citing Victorian-era authors to "prove" Islam. I think that Muslims will eventually move on with this as the rest of the world is, but it might take a little more time.
Some of the social changes that came with technology, especially regarding gender roles or the democratization of knowledge, have been uncomfortable and contentious; and often, there is a conflict between having a traditional paradigm in mind and the real-life lives that we live. I think this will sort itself out and Islamic thought will adapt to the new realities we are living in.
That being said, I suspect that many things that have been "traditional" over the in various places will continue to be so. Things become "traditional" because they are functional (even if not ideal) and in some places there will not be a big change.
Also, (b) I think that environmental concerns will become a top priority, and the need for basics such as drinkable water and clean air will overshadow many of the issues that are considered important today.
I HOPE that there will be a reduction of poverty and warfare in Muslim-majority countries and improvements in political justice. (This is not to say that every Muslim-majority country is dimsal but we are aware these are problems in much of the Muslim-majority world.) Really the political situation seemed to hit an all time low in the 20th century so one hopes it can't get much worse.
Regarding Islamic thought, I expect that there will be a widening gap between (a) literal/traditional interpretations of Islam (for instance, literal derivations of fiqh) and (b) "reformist" views which promote things such as deriving law from the spirit of the text, rather than the actual text, or focus on social contextualization.
There are just a couple thoughts, and I am sure others will have thoughts as well!