Do you think having friends is a requirement for a happy life? It's not strictly necessary, but they are a positive factor, and most people will not be happy entirely devoid of friendship.
Having a partner is a friend you commit to and are closer with than other friends (generalization, sure). I have friends who I would not support through depression, but I would support my partner through depression. Needing someone like that is not unhealthy. It will be difficult to find someone willing to give the same commitment to your friendship as to their partner (generalization again).