Communication Respect Humor Similar Sense of humor Friendship, not necessarily in that order.
Intimacy is also important and I don't mean the type of intimacy that you get from the bedroom. I mean the type that comes from feeling that you and your secrets and your fears are safe with this person. That this friend is your best friend and you can share anything with him/her and it will be safe.
The five most important things in a healthy relationships is honesty, love, trust, support, and of course respect. Make sure he/she does all these things to you. Because if he/she doesn't than he/she obviously don't like or want you.