Whether we can have trust on the children or not we have to keep a watch over them till they grow up into responsible adults. The art lies in doing this without making it too obvious and at the same time allowing them a progressive freedom to experiment and explore. It is not a lack of trust but a prudence and vigil that is needed during growing up as children are not fully equipped to deal with number of issues. This has to be done reasoning out various issues of life and our responses to various situations.
What you need to do is discuss things with him and if you observe certain signs that may indicate stress such as social withdrawal, sleep disturbance, lack of interest in things, too much addiction to phone or strange odd statements, then one needs to ask frankly if all is well.
It is also not a good idea to give too much pocket money and provide all kinds of luxury and comfort to a child as it may make the child lazy and prone to impulsive action due to the habit of needing immediate gratification. The tendency to express love by giving food and buying him expensive things spoils them..
However as the child grows through adolescence one has to accept and hence ignore certain exploratory and experimental behavior. Educate but do not strap a child. Teach him but give him freedom of choices. Only two things should raise an alarm, – signs of depression and behaviours suggesting drug abuse of any kind.