Help! need advice for an issue my girlfriend and i are having.?

My girlfriends and i had a heavy argument the other night and she went to a very sensitive subject that made me cry and at that moment she didn't even feel sorry.. she really hurt my felling and she didn't care. then a couple minutes later she regrets its and apologizes in tears.. So anyways today she felt like she had to tell her best friend what happened that night. I asked her not to tell her cuz i don't want her friend knowing a personal moment of weakness that i had..so regardless she went out and told her.. and i got upset cuz she went against me. so the question im trying to ask is am i over-reacting or should i be rightfully mad that she cant respect what i am telling her. (by the way this isnt the first time she has done this went against my back & word knowing how i feel and that i am a very personal person and to open up to her is hard for me, and now i want to end it with her.. so am i in the right or wrong?, am i just being overly sensitive) O by the way the thing she said was mean as hell, never expected her to say **** like this.. cuz i thinks she is pregnant and she is scared... so i jokingly told her that she was and rubbed her stomach and that got her upset, then she tell me that if she is pregnant with my baby that she will kill it and mine alone.. so basically if she was pregnant by another guy she would keep it. but not mine...she said she wouldn't tell me she was pregnant. Thats a really ****** up thing to say or am i alone in this? is it something to cry about? i feel foolish.. need help.. im 19 and so is she and been together for about 3 months.