pi isn't even a fraction. like, it's actually an important thing that it isn't

The problem is, that's exactly what the ... is for. It is a little weird to our heads, granted, but it does allow the conversion. 0.33 is not the same thing as 0.333... The first is close to one third. The second one is one third. It's how we express things as a decimal that don't cleanly map to base ten. It may look funky, but it works.

Pi isn't a fraction (in the sense of a rational fraction, an algebraic fraction where the numerator and denominator are both polynomials, like a ratio of 2 integers) – it's an irrational number, i.e. a number with no fractional form; as opposed to rational numbers, which are defined as being able to be expressed as a fraction. Furthermore, π is a transcendental number, meaning it's never a solution to f(x) = 0, where f(x) is a non-zero finite-degree polynomial expression with rational coefficients. That's like, literally part of the definition. They cannot be compared to rational numbers like fractions.

Every rational number (and therefore every fraction) can be expressed using either repeating decimals or terminating decimals. Contrastly, irrational numbers only have decimal expansions which are both non-repeating and non-terminating.

Since |r|<1 → ∑[n=1, ∞] arⁿ = ar/(1-r), and 0.999... is equivalent to that sum with a = 9 and r = 1/10 (visually, 0.999... = 9(0.1) + 9(0.01) + 9(0.001) + ...), it's easy to see after plugging in, 0.999... = ∑[n=1, ∞] 9(1/10)ⁿ = 9(1/10) / (1 - 1/10) = 0.9/0.9 = 1). This was a proof present in Euler's Elements of Algebra.

pie never actually ends

I want to go to there.

There are a lot of concepts in mathematics which do not have good real world analogues.

i, the _imaginary number_for figuring out roots, as one example.

I am fairly certain you cannot actually do the mathematics to predict or approximate the size of an atom or subatomic particle without using complex algebra involving i.

It's been a while since I watched the entire series Leonard Susskind has up on youtube explaining the basics of the actual math for quantum mechanics, but yeah I am fairly sure it involves complex numbers.