As all of you know, in the Milky Way galaxy, the Solar System revolves around the Milky Way to complete the Galactic year (because we have the supper massive black hole in our Milky Way galaxy) then the Earth revolves around the Sun, and the Moon revolves around the Earth. This is due to Einstein's theory which suggests that anything with mass in the universe will bend the spacetime fabric and due to its gravitational pull, another object will attract and they will revolve around that object because that object bent the spacetime fabric.
I read somewhere about the collision of Andromeda and the Milky Way galaxy in some billions of years. According to my knowledge if objects in galaxies will have some mass then the galaxies will have some cumulative mass.
So my question is simple: according to Einstein anything in the universe with mass will bend the spacetime fabric. Will the Milky Way revolve around the Andromeda galaxy or vice versa?
So if they will collide then why won't they revolve?