My thinking is that, with infinite time, all mass will eventually be
There are two competing factors here, gravitational attraction and universal expansion. Generally the later of the two is "more powerful" - from what we can see, the matter in the universe is too little and too spread out to have enough collective gravity to overcome the existing expansion. So at the universal level, no, we're not going to be one big black hole.
But that's at the macro level. At smaller scales there's huge variations in the spread of the matter, and there's areas in the universe where there is enough matter, and gravity, to overcome the expansion. So in the far future, the universe will be these little blobs of matter with huge amounts of space between them.
Now one example of a system who's gravity overcomes expansion is the Milky Way. So imagine the Milky Way far in the future, will everything be sucked into the black hole in the center?
Nope. Orbits still exist. The Earth has been floating around the Sun for a good 4.5 billion years now, and we're not in danger of falling in any time soon. That was not the case 4.5 + 0.5 billion years ago when what is today a nice clean Solar System was filled with junk. Back then things were crashing into each other all the time, and those collisions result in all sorts of random trajectories, some of which ended in the Sun. But after a while anything that wasn't roughly co-planar collided out and we're left with the Solar System we have today.
So if you roll that forward long enough, what you end up with is a universe full of black holes and other objects like neutron star cores, all orbiting their collective center of mass. These will be spread out a LOT from the other collections, much more empty than the universe today. Astronomy will be rather boring.