It's quite long

1. Clovis Ash-heart was born into a wealthy family in the kingdom of Bleak-Wood.

   His family was renowned throughout the kingdom for being the kings right hand on the council. Advising him and directing him through hardship. It had been that way for generations. Clovis was raised alongside his sister Rose to be prim and proper, obeying the rules ready to take on the next generations of council. But Clovis hated this. He hated the lessons, the fancy dinners, the etiquette lessons. He hated it all. He desired a world away from the conformity and monotony of noble life.

    

   Little did he know though that his family was not any ordinary boring noble family. No they were much more than that. His family are actually part of a hidden cult that spans continents, they worm their way into a position of power in the monarchy and slowly take over, pulling the strings while the ruler remains a puppet. This cult worships the god Ilsensine, the master of the mind and they have members in nearly every country their populous nearly in the thousands. Their goal is to awaken their master and let him take over the mind of everyone in the forgotten realms.

    

   They do this by infiltrating a kingdom, letting Ilsensine take over the mind of the ruler in his locked dimension and begin pulling the strings of the kingdom to Ilsensine’s will.

    
2. Another family who had ties to this cult was the Shatter-Star family. Who had an eldest son named Laurence. Laurence and Clovis fell in love and got engaged. Neither family fully approved of the relationship but accepted it as an alignment of power between the houses.

   Clovis and Rose (Yes and Laurence) are both totally unaware of this and were going to be told on their 22nd birthday. The only issue is Clovis started rebelling, he started by partying and kept expanding his acts of non conformity to the point where they started creating public scandals. His family considered him a liability and officially exiled him. Clovis was going out into the world broke and alone.

    

   Until his sister Rose came to help in an act of kindness she gave them money and helped him leave the manor safely. Also officially calling of his engagement for them. Her final goodbye was said as “I know you’ll fulfil a great destiny brother, goodbye” Clovis began wandering the forgotten realms as a bard singing about the past heroes, putting on a happy front but in actuality he regrets his decision deeply. They miss their sister and their fiancé but he knows he can’t go back. Because of the embarrassment. So now he wanders unaware that both his sister and ex fiancé are being forced into a cult that might threaten everything.

It is a interesting backstory, there is a potential BBEG from this as well or a character arc boss that may span from a hundred members of cults.

Ah! Sorry for seeing this late and thank you! I wanted to give our DM a lot of stuff without going overboard

My only suggestion would be to talk to your DM (if you haven't already), as this backstory could quickly give your PC "main character syndrome". Having such world changing events directly tied to your backstory will make it either such that your DM is sorta forced to incorporate a lot of it into the main plot - making you essentially the 'main' character - or they ignore these world changing events which would feel bad. 

Basically, if the rest of your players have equally grand- scaled backstories and the DM is cool with it, awesome! There's some juicy hooks in there for great storylines. Just ensure that there's enough for the other players to tell their story as well.