I am feeling this weird bond with my cousin, it makes me want a sibling?

I can understand that you feel like you missed out on having a bond with a younger sibling, but you have no idea how many annoying, worrisome, and angering situations you missed out on. I have never personally witnessed a pair of siblings who didn't halfway hate each other. When you have to actually grow up together, there's usually competition, jealousy, fights... So, if you think of siblings as being instant friends, of course you're going to feel like you missed out on something good. If you think about it in a more realistic way, you might be more accepting of having been an only child.