Scared

My boyfriend and I have done a lot of sexual stuff lately, as we do not get to see each other often and he is leaving soon because we are long distance. I am afraid that my mom somehow knows and is going to yell at me about it once he leaves and I am also very emotional about his leaving. I feel that if she knew she would talk to me about it and get angry at me, but she could be holding back until he leaves, as she doesn't like to show how mean she can be when we have company.... I'm just very worried and I am very upset and emotional 
Update: I'm 16