On being utterly fucking shit at learning German

I've lived in Austria for over 2 years.

My German is shit.

I understand a fair bit and my vocabulary is alright but I can't speak it much past the basics, and 90% of what I say makes me sound like an idiot because my grammar is absolutely terrible.

I've tried and tried and recently went back to basics and bought a book explaining German grammar for absolute beginners but I really cannot absorb the information no matter how hard I try.

Basically what I fail at is this:

There are 4 cases in German (nominative, dative, accusative and genitive) as well as 4 basic ways of saying 'the'. This essentially means the word for 'the' could be any one of 16 depending on the noun used and its context within a sentence.

The cases themselves are confusing. I have no idea what those four terms mean even in English.

Last night I spent 2 hours reading the same 5 or 6 pages and learning the rules before attempting a few basic exercises.

I got 18/68 right, and a lot of those were through guesswork since even after studying for all that time I wasn't sure if I was applying the rules correctly.

It is completely baffling to me, and entirely frustrating since I am generally pretty good at learning new things from scratch with a bit of practise, and I'd say my grasp of the English language is above average.

When studying or being tutored I just cannot understand most of what is being said and all the grammatical terms and rules end up just floating around and making absolutely no sense to me. I kind of hear it, or read it, as follows:

"You have this, this, this and this. When this is said like this, or in a sentence with this like this, you need to use this word for this."

My girlfriend thinks I am overthinking things when attempting to learn but that's what comes naturally to me. For example in English, although I may not know all the rules or grammatical terms involved, I know how to apply them naturally, whereas in German I don't and therefore want them to be explained in detail, which both Vicky and my former German tutor were unable to do.

Here is a stripped down example of a typical exchange between myself and my tutor:

"Why does ein change to einen here?"
"Because of the case"
"What's a case?"
"The way it is used in the sentence"
"How do I know which case to use?"
"You just pick it up"
"How?"
"You just have to practise"
"How can I practise if I don't understand what I'm practising?"

*she explains the cases for the 50th time*

"Do you kind of understand it now?"
"I think so"

*I successfully construct a sentence based on different cases*

"Good. Now try another

*I fail*

"Why was I wrong that time?"
"Because of different nouns used"
"So there are rules to learn but sometimes the rules don't apply and I basically have no way of knowing when they will or won't?"
"You'll pick it up"
"How?"
"You just will, with practise"

And so on. It seems like I can study and study, but as soon as I get something wrong, I don't understand why, and I discover that what I thought I knew I basically just got right with trial and error.

Nothing has ever made me as angry as my inability to learn German, and it's made worse by the fact that other, dare I say less intelligent people, seem to be able to pick it up with relative ease.