How to keep from telling parents something?

Okay so i have been having fun online wiith an almost boyfriend flirtatious texts and stuff and been having a lot of fun. Now i don't want to tell my parents about this until well im 16 now and their uptight so how about 116! anyway sometimes i can slip and spill my guts out to my mom, and i dont want to betray this guys trust. so any tips on how to keep my lips zipped!