In human nature we trust to often with the wrong individuals. In building up trust with someone in a relationship if friends or a significant other there must be boundaries.
You can only tell with time and life experiences. It's almost always a trial and error thing.
This post was edited by Zack at June 14, 2017 11:47 AM MDT
The only time I ever trust someone completely is when I feel that, if they ever turned out to not be who I thought they were, then everything I knew to be true would be false and my entire perception of reality would be a lie. In other words, I analyze someone for a very long time until I can predict their actions with 99.99% accuracy before fully trusting them (with anything). That being said, different people who aren't as trustworthy can still be trusted with different things that aren't as important. It's a risk/reward, or cost/benefit, kind of deal.