Technically you do not have to but it might be better if you do. It all depends upon how serious the relationship is and how long it has been going on for. Some people do not like to tell their parents that they have a relationship until they have been in the relationship for a while. This is because in the past they may have told their parents about their current partner but then they may have split up soon after causing embarrassment.
Overall if it is a serious relationship then telling them would be the best option. They will trust you more if you tell them things too and that will make your life a lot better and a lot easier.
Overall if it is a serious relationship then telling them would be the best option. They will trust you more if you tell them things too and that will make your life a lot better and a lot easier.