I think they can't help it. Even if you get really close to them they instinctively know that if they are completely honest with you that you probably can't handle it. And they're probably right
But you give them companionship and someone to talk to and/or confide in. I think that's sorely lacking in their lives
Are these just friendship type relationships or is there ever more? If you're just hanging out casually then there probably won't be any trust issues. If it's more then that then I'd find it hard to believe that there's
% trust (unless you're okay with a totally open relationship)
Surprisingly I've found that even without asking any awkward questions I still get told lies quite regularly. That's something I don't fully understand. Why volunteer info that's not true when there's no reason to?