Sex is fun and in a relationship of two loving adults, can increase that love. However, like most fun things it is not without its risks, and should be treated with maturity. It is important to look after the health of yourself and your sexual partner by using contraception, to avoid pregnancy and the risk of sexually transmitted disease.
Mistakes can happen and you do not know what the consequences might be when you are not thinking rationally or are too guided by your desires rather than your head. This is just a part of growing up, and life would not be possible without making a few mistakes along the way.