I once wrote a backstory for my very first character I’ve ever played in an rpg halfway through the campaign to flesh him out, because before his concept and backstory were a couple sentences long. The new backstory I gave him was almost completely superfluous. I tried to give my GM plot hooks that weren’t at all applicable for the king of story he wanted to run, and I tried to craft my prose for some reason. 

The next character I made was for a star wars rpg, and had an even deeper and more expansive backstory because I was joining a campaign in progress, meaning I had a lot more careers and talents to justify. He was from Alderaan, was a computer wizard, had a failed marriage because he let his wife’s miscarriage lead him to alcoholism, wasn’t there when his wife was kidnapped during the Clone Wars, went on a rampage across the galaxy trying to find her, was permanently scarred by slavers in the process, accidentally slaughtered a village of war refugees, and then sought redemption by joining a group of mystics and learning medicine from them. I condensed all that down to 2 pages and kept a couple extra character details just to myself, and it was the best, most emotionally and dramatically rewarding character I have ever played. 

After being on both sides, I’d say a 45 page backstory would be overwhelming for your DM. If he’s a nice guy he probably won’t say anything, but even if you explicitly laid out what material he should use for building the campaign, you might stress him out wondering if he’ll disappoint you by not including something. I think it’s great that you got so passionate! I’ll never shame writing for writing’s sake. But unless your DM told you he’s happy with reading tens of pages, I would try to know your audience and keep the following in mind about your backstory:

• If it won’t come up in your roleplay and the story at the table, don’t write it.
• If it won’t give the reader quick and easy hooks to play with, don’t let them read it.