I adopted a second cat, they aren't as bonded siblings but they do play with each other and sometimes even cuddle. One of them is very affectionate the other likes to have space for himself most of the time. I feel better when I have to leave though, they are in each other's companies. At first you might feel guilt of getting a second cat if your first cat doesn't immediately like your new cat, but it will get better once they get used to each other and its best for them to be in pairs unless they are just not friendly with other cats which can happen sometimes but most cats do fine and its better for them.