Well I would say the effects could be having sex when they are not ready for it. And you know what could happen then. High school teens should not be in a relationship if you ask me.
I would say the effect on a boy-girl relationship would be no honesty. . . .so be honest to each other if you both wish to go on with your life TOGETHER. . .
Honestly, it is almost impossible to tell. It really depends on the girl. If the girl is the popular type who gives lots of hugs:-she is most likely just being her flirty-self, does that often...