But... how can a multiverse that is infinite and vast get sucked into just one tiny black hole?

I’m pretty sure the Black Hole is Supermassive, rather than tiny. Remember that the Green Sun was twice the Mass of the Universe and still SOMEHOW didn’t collapse into a Black Hole- The Breach has absorbed the Green Sun and is tearing the Furthest Ring apart which is arguably only adding more mass to it. I don’t know but, a Black Hole over twice the mass of the entire Universe sounds like the kind of thing that could rip reality at the seams completely and absolutely.