So this question is going to have a lot of "depends on" context?
But some ideas are:
Your friend started dating someone so they neglected you and now that they broke up months later they start talking to you again
Your friend finds new friends to hangout with etc. they end up not being friends with them anymore
They stopped talking to you for some reason (boredom, lack of interest, etc.) But something tragic happens to them and now they are at your feet
I think yall get the gist.
What would you all do? Do you start talking with your and pretend like nothing happened? Do you give it some time before bringing up their absence? Do you let them know right away? Do you ignore them? Thoughts that the same will happen again? Thoughts that you're being used? Etc
Implication is that your friend stops talking to you for weeks or months or maybe even longer etc. Long enough time that makes you feel like "I thought we were friends"