My rats brother was put to sleep today, how am I going to make sure he's okay?

Hello, today (5th december 2016) my rat Wilson was sadly put to sleep after being diagnosed with Mycoplasma pulmonis on Saturday (3rd of December 2016

Hello,
today (5th december 2016) my rat Wilson was sadly put to sleep after being diagnosed with Mycoplasma pulmonis on Saturday (3rd of December 2016) and I was just wondering how I can keep his brother buday from becoming depressed now that he's gone? I'm looking in to buying new rats soon but I've read up that it's best to keep them separate for a while and introduces them slowly. I'm soooo worried about buddy because all he's ever had is his brother as a cage mate and his death was so sudden because he was fine on the 1st slightly squeaky on the 2nd, really sneezy and squeaky on he 3rd, then on the 4th his breathing got heavy then by the night he couldn't eat or drink. So within 4 day (Saturday and Sunday being on antibiotics) he just couldn't fight it.
Is he going to get depreased?
Is there a chances he could be come really ill to?
Is there a certain way I shold introduction young rats to a 1and a half year old rat?

Please help, this has never happened before as both of my rats normally go around the same time after 3 or 4 years.

Many thanks,
Sam.

or:Hello, today (5th december 2016) my rat Wilson was sadly put to sleep after being diagnosed with Mycoplasma pulmonis on Saturday (3rd of December 2016) and I was just wondering how I can keep his brother buday from becoming depressed now that he's gone? I'm looking in to buying new rats soon but I've read up that it's best to keep them separate for a while and introduces them slowly. I'm soooo worried about buddy because all he's ever had is his brother as a cage mate and his death was so sudden because he was fine on the 1st slightly squeaky on the 2nd, really sneezy and squeaky on he 3rd, then on the 4th his breathing got heavy then by the night he couldn't eat or drink. So within 4 day (Saturday and Sunday being on antibiotics) he just couldn't fight it.Is he going to get depreased? Is there a chances he could be come really ill to? Is there a certain way I shold introduction young rats to a 1and a half year old rat? Please help, this has never happened before as both of my rats normally go around the same time after 3 or 4 years.Many thanks,Sam.

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