Is my step father invading privacy?And Should i tell the Truth?

my step father pays for my cellphone bill.he made a deal with my phone company so where every text or call i make he can see what i said or who called.It was no big deal right until I started text to my friends that were boys which my parents told me i couldn't text them when first got it(i know me being hard headed) now my step dad has seen my texts and contacts from boys he go's and tells my mom i have a boyfriend the night after my mom and I had a conversation(this dates and having a boyfriend)so the night we all had a discussion/argument he tells my mom about the text messages i had with the boy i liked so when my mom asked me if i did in a demanding voice Iied and told her no i dnt have a boyfriend because i was scared.know my moms mad at me and doesn't trust me because i cant tell her the truth.i know i should sit down and tell her but shes almost 8 months pregneat with her 5th child very emotional and mean and doesnt trust me because i cant tell the truth PLEASE HELP!!!!!!!!!!! :(