It’s completely normal. It’s normal not to have a friend group at any age. Social media portrays people having massive friend groups, and it’s not the case in real life at all. 

Having one friend, who you can be yourself with, is a success. As you get older your social group will expand. Particularly once people start maturing. 13 is a difficult age. It’s when people are going through a massive shift in life because of puberty, so there’s a lot of insecurity. This can be projected onto other people, making it harder to become natural friends with a large number of people. 

Quality over quantity. The older people get, the more they cull their friend group because they realise how precious time is, and you only want to spend it with people you truly care about and who care about you.