Cross claims often end in a dismissal of the charges but the seriousness of the charges and prior history are often taken into account. It is totally within the discretion of the State's Attorney's Office whether to drop the charges or not.
There are many ways either case could resolve. Often in cases like these, both parties are able to invoke their Fifth Amendment privileges against testifying. Because both of you would potentially incriminate yourself by testifying against the other, you cannot be forced to testify in this case. If the prosecution does not have any other evidence of the crimes, the cases will be dismissed. If there were other witnesses or other evidence, however, the Commonwealth could go forward without your testimony. You need to decide what you want to see happen in your case. Do you just want to see both cases go away as soon as possible? Then talk to your defense attorney about a joint invocation of your Fifth Amendment privileges. Do you want to pursue the charges against your ex-boyfriend but have the case against you dropped? Then have your lawyer talk to the Assistant District Attorney prosecuting the case about your wishes. If the charges against you are as thin as you say, the ADA may decide to drop the case against you and proceed against your ex.
Either way, talk to the attorney appointed for you as part of your criminal case, or, if you haven't yet, hire an attorney to represent you.
If you both do not testify against each other, and there are not other witnesses or other evidence to the crimes, then the prosecution will not have enough evidence to proceed on the day of trial and both sets of charges will be dismissed. You both may have a valid 5th amendment privilege to refuse to testify against one another.
The fact that you were not able to tell your side of the story when the police arrived will not be used against you at trial.
The fact that your ex has a prior record will not be used as evidence against him at trial, as it is a form of inadmissible evidence.
You are in a tricky situation in that one person's (X) refusal to testify the other person (Y)is usually conditioned on that other person's (Y) reciprocal refusal to testify. However, somebody has to go first (say X), leaving the remaining person reliant on Y to not testify against X.