system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If the universe is expanding and the distances of each galaxies get larger over time then why is our own galaxy (Milkyway) will collide with another galaxy (Andromeda) in the future?
gpt
Andromeda is part of our local galactic cluster, which is still bound by gravity that’s stronger than the expansion force.  Other galactic clusters are getting further away from us but the galaxies within our own cluster are not, or rather are not due to expansion. 

Galaxies within other clusters are the same, they remain locally bound to each other.  Expansion is acting at extremely large distances only at this time.