Typically people will give a broad answer to the question and say a variation of "Good, Great, Busy" etc and then pick out one specific thing that has happened lately to bring up. It's not meant to be taken literally. Examples include something going on in their life, a new book they are reading, a sports game, movie or TV show recently watched or anything else that you would want to share with the person. Typically, if you don't know a person very well you give a more broad, generic answer. If you are close with the person asking you can be more honest, especially if everything is not going well and would like some support.
Sound
Clarify status of relationship.
Fine thank-you.
my life is going well
Say what you are doing, possibly in a banterish way.
tell him how you feel about him.
huh? this question is weird. it isn't really clear what you're asking... If you meant to ask: "Someone asked me on facebook, what makes me think he doesn't like me; what should I reply?" then you should reply with whatever it is.
What's up is a popular slang and is used only in informal English. what's up basically means "how's everything going on?" it is a general question and is asked when you a meet a friend etc. it is usually the first question of the conversation. you can just reply casually.
When I am asked how I am, I usually reply that I am fine.
When asked what's up your response can be as simple as not much. Or you can go into detail about what you are doing.
Let's say somebody asked me who is this, then I'll reply this is cloillia
Say yes or no.