My pet rat just died and im worried about my other one getting lonely.?

i had 2 rats and one of them had a problem where he kept having fits and seizures, there was nothing we could do but one day he had a particularly bad one and his back legs stopped working, we had to take the other rat out the cage and let him eat because he was so week he couldn't get to his food before the other rat. Then his tooth started growing oddly and it was pressing into his check and causing him pain so we took him to the vets and spent �30 to have it trimmed back. We thought he would be fine but then the tooth grew back oddly again, we took him to the vets the have the same operation but he couldn't withstand the anaesthetic and died. Now im really worried the other rat might die of loneliness because his companion's gone. please help me. :(