why he isnt telling me that he talks to "her"?

[923]

Hi! So I have this boyfriend for about half a year now and he has always been telling me how much he loves me and cares about me. He leaves his friends just to hang out with me. I recently had this idea, to activate my fake acc on facebook with pictures of a girl I found online. These photos are not trying to attract anybody and aren't showing any skin. I tried to troll him (i would tell him the next day that it was me) by chatting with him (he trolled back) and when I signed off he left 'her' a message by telling her im so sorry about today I didnt mean to say anything of what I ve told u etc. I really started getting serious of this and I started playing with this situation since last week. He has never told me that he talks to a girl named "..." and when he doesnt answer really quickly on my original account he lies to me "i went to drink some water,sorry" while he was talking to my fake one. P.s. He has told "her" he isnt hitting on her because he has a lovely girlfriend and that made me feel glad.
I dont know what to do. Should I keep on doing this? Or continue, just to make sure he is really into me? And why isnt he talking about that girl to me? I am really confused and the worst part is that I was going to tell him I was joking but....
Thanks for your time everybody! x