My girlfriend has a std (im a girl) and ive started bleeding after sex, like she does. what could it be? is it curable what symptoms could there be

Unsafe sex: Your symptoms could suggest any number of several STDs including a cervical infection. The safest thing to do would be to abstain from having any additional sexual contact. See your medical provider as soon as possible and get the proper examination and testing done. If left untreated in could result in PID or worse, infertility. Your condition should respond to the proper antibiotic medication

Blood=tissue injury: Bleeding as a symptom is no more specific than that. You did not provide the name of the STD, or elaborate more on the symptoms. Form that minimal information it is impossible to say whether you have a treatable problem or not. You both need to have a formal evaluation and testing as soon as possible. Some curable issues can change to "not" if you don't start treatment in time.