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I am not trying to sound picky...but you have a few comma splices in your letter. Comma splices are when you put two independent clauses together with just a comma. They need to be separated by either a semi-colon or a conjunction plus a comma.
For starters after "I regret so deeply not being a loving partner to you," I'd end the sentence instead of dragging it on. You want to avoid a run-on sentence. I'd avoid saying "so bad" but it is not necessarily a grammatical mistake. It depends on the vibe you're shooting for. If you desire a clean cut professional vibe I'd revisit this sentence. I would also edit your contractions. In the same sentence, "I’m in love with you and I want you in my life so bad enough that I’m willing to go through all of this pain." I believe a comma is needed. Besides that I'd say you're good to go. Also I enjoyed reading this, I'm quite the fan of angst and I think this had an angst touch to it ^^