Roommate and Her Cat Moving out - Will my Cat be Ok?

Hello,

This is sort of a strange topic and I'm not sure if this is the right section for it, but I'm going to give it a shot.
My current roommate and her cat (aged 2) are moving out next month to move in with her boyfriend.
My cat, Lily - aged 5 - has been living with my roommates cat since March. They bonded pretty well really quickly (Lily grooms Joey and they share space well).

Does anyone have any tips on how I can make this transition as easy as possible on my Lily?

Thanks so much!

The same thing happened to me a few months ago. What I did was get a kitten and had all three cats for a month or so. When the roommates cat left it was not as traumatic because there was still two cats!