That's right. This is the mark of true camaraderie. No one can ever break this. Even if Dan-I makes new friends with others, she'll always have Ban and the others by her side.
And I get why Dan-I sometimes feels the need for reassurance. She's still young and holds a lot of insecurities in her. Every now and then, she needs to get that reassurance so that she can renew herself. And honestly, they know about her deep fear, so they will always be there for her.