but that's where you quickly find a grey area. How do you know when they are sure? If you're not sure that they are sure, does that give you the right to continue giving that person "positive encouragement" when they don't want it?
It's because of these grey areas that, in general, it's easier to accept a persons actions and decision at face value and give them the interaction they desire. If you do this then I think those people will naturally go towards the decision they want to make.
Edit: It's also the issue with becoming personally close to people here on the site but at the same time, if we want to be taken seriously and have people respect us emotionally for choosing to die, then we have to do the same for our peers here, as hard as it can be. You're absolutely right that you can't choose to live again once you're gone and I also feel that it's important people are fully aware of the consequences of their actions, but all of these small variables generally need to be attended to by the suicidal individual and not a friend or guide or saviour.