I've been inactive for a while, logged in to find my main pet's name to now have an underscore and numbers after it, and someone else has a pet with my pet's name. Is there any way I can get it back?

I'm afraid you won't be able to get it back, unless the new owner has also gone inactive for a year. And if you're talking about GLaD0S, I'm afraid that's not the case. I'm sorry about that. :(

But the good news is that you now have a free name change! You can change your pets name to anything you'd like. :) Normally this costs 500 CSC, but when your pets' name is taken while you're inactive, you get to change the name for free.

If you need ideas for a new name, might I suggest looking at lock plz! or Available Real Word Pet Names 3.1?

Unfortunately after a year of inactivity, anyone else can rename their pets over your existing ones. You do get a free rename if they get name bumped (you can change in through your pets page), but chances are you have to find another pet name as they are currently unique.

thank you both. it's unfortunate but i guess i will have to rename her.

I had this happen to a pound pet, (I think it was from a Japanese (Manga?) series (or comic?) I just took the letters and renamed her. It does kind of suck to be away, specially if you are ill to find someone has your pet's name. I would've been ok if they said "sorry, but I must [insert brief reason why] have this name! ...yoink." :D