How could we know that our friend lies to us?

I have a friend called A. She introduced me her friend who is called B. I've never met B before. We're a friend in messages and e-mails. Last November, he went to America. Then his friend, C, mailed me. I've also never met him before. We are friends. C like my best friend, D(they also never met before) . And B likes me.. (so confusing!!) The problem is.. there are no proves that they are exist!! I've checked B's IP address. And you know what?? He lives in Surabaya, Indonesia. Well, I actually live in Jakarta. Lots of crazy things happened in my life since I know them. Example, B was almost jump from his top of the house because of ME!! I even didn't hurt him, I like him! And also, C, was fighting against his unknown friends because they all like D. Me and D don't believe them!! The IP address is the prove that they aren't excist! But A, the one who introduced me, doesn't want to tell us the truth! Now, how could I now the truth? Because (NOW) they seems like they are excist.. hh

How could we know that our friend lies to us?
hm this is a very hard question...well ask them why are you doing this and see their face if they dont answer or didd not say the turth and show your feeling to them and if they still never tell you said to them that you dont want to talk to them... well this happen to me too i did that.. and sorry about this :( i dint mean to said this but good luck!