Should I explain my girlfriend situation to my ex? Should I explain the Ex situation to my Girlfriend? BOTH?

My ex girlfriend tried adding me on Facebook. I ignored her request. I didnt tell my girlfriend. the Reason is because she gets mad and worried about situations like this, and I already made the right decision of ignoring her request. My girlfriend has reason to to get mad or worried because our first year of our relationship, I still had feelings for my ex (same one trying to add me). I had he urge of messaging my ex and explaining why I couldnt be her friend, I dont want this to a future problem or there to be any tension. But i havent done that yet because Im scared that my girlfriend might find out and it would make the situation much much worse. My girlfriend is just starting to trust me again. It's been hard for her. I dont want my ex to get the wrong impression. I dont know if I should tell me girlfriend about it.. Tell my ex girlfriend the sitation. or leave it as is. Not Tell ANYONE and just move on.