...after doing some mathematical calculations for several days i now realize that black holes will at some point regroup and consolidate into one which will suck up the galaxies in rapid succession until we are right back at the origin of the big bang.
You may want to check your math.
Besides, the question whether the universe will expand forever, come to a standstill or eventually collapse again is still undecided. The mass of all visible matter (which includes black holes, ironically) is insufficient to stop the expansion. Even if the universe was so balanced that the expansion would come to a standstill (which is nothing but a fringe theory at this point) and all the galaxies were the be sucked into their own black holes (which is unlikely for a whole host of reasons) all the black holes of the universe would retain their momentum, and orbit each other.
SURE, their orbits will decay as their relative motion to each other deforms spacetime around them to create gravity waves. But that is such a slow process except for the last moments that it will take several orders of magnitude of the universe's current age before the last two black holes might merge.
