Yes, it gives me headaches too
Yes, according to the theory, that is exactly what happens, there would be billions of alternate universes with billions of alternate "you" for every single decision you took in life. (I'm not saying I agree with it, in fact far from it. Just stating what the theory is about).
This theory was developed to explain particle movements at a quantum level but the reality is that we are all made from quantum particles (including our brains) and everything we do creates movement of these quantum particles and therefore splits the universe. Pretty crazy stuff.
I have read a new theory which I believe makes more sense, which states that multiple universes do exist but they are not created by "quantum splitting" instead they are created by black/white holes. Where a black hole will at the other end create a white hole where matter is poured into a new universe(creating a big bang). As far fetched as this seems, it would explain the problem of the quantum particles without the nonsense of splitting universes.