If I can easily consider my friend's house as a place to sleep a night when I need it as well as I do with my relative's houses while travelling - that is one o

If I can easily consider my friend's house as a place to sleep a night when I need it as well as I do with my relative's houses while travelling - that is one of crucial signs. Another one is similar hobbies when we are helping each other - this sign might be useful even for online friends you have not seen offline. If one of signs is true - this is my friend; both true - this is my best friend.