How Do I Know If He's Stopped?

A friend of mine is trying to kick a long term coke habit. I'm trying to help him, to the extent that I can. He tells me he isn't using anymore, except for when something happens that makes him unable to deny it. The last time that happened was about a week and a half ago.

Last night, we were at dinner and he went to the bathroom. He came back, and within a minute he had a nosebleed. He told me that he had blown his nose in the bathroom, and must have blown it too hard. He said that the nosebleeds can continue, because of the damage to his nose from his years of use/abuse. I don't know what to think, or what to believe anymore. I kind of do believe him, because he's ususally a lot more intense during arguments when he's high than he was last night. But, I just don't know what to believe any more, having been lied to by him so many times before.

Is it true what he said about the nosebleeds continuing even after the use stops, or am I just being dumb to believe him yet again? (For what it's worth, I think he really does want to stop and he's gotten himself into counseling for that purpose.)
First of all can I say well done for helping someone with a habit,& remaining their friend. It is true about the nosebleeds, so please dont be too hard on him, but having said that, I would be very aware about the amount of times that he goes to the toilet or anywhere else that he can be alone for a few minutes & use!
People can be very creative in making excuses to "leave the table" or use their mobile phone....
The truth is that he has to have a real & valid reason to make him stop, this may come in many way`s & I really hope that he is genuine about staying clean.
Please keep him away from situations & people that he was in when he previously used.
My prayer`s are with u both. x