Over two years ago my ex assaulted me. Charges were filed but I did not testify so all three were thrown out. Then he almost killed me so this time I am going to testify. One of the cases that was trialed in the prior cases I did not tell them that he also rapped me several times so it technically the act was not tried. Can I now bring that incident up for new charges? I have counselling records from over two years ago that would prove that it happened just two embarrassed so tell police. Can I now give that as evidence because it was not included as evidence in the case back then?

You really need a LAWYER, who may tell you it isn't a good idea. Why? Opposing counsel will rake you over the coals for not telling the police, not going to the ER or even so much as getting a morning after pill, not including it in old charges, and (the icing on the cake) not testifying. You will be painted as a tease, or still in love, and here you are still allowing him in your life. Counseling records? All they 'prove' is that you said certain things; where's the rape kit? And so on! And a judge might disallow it anyway, in a pretrial hearing. So why are you asking here instead of asking your lawyer, or the DA's office if they pressed charges?

I realize that I sound harsh, and that you just want to know if you should bring it up, and may not have easy access to the lawyer handling this, especially in a big city.
Also that it's hard for you to bring the subject up.
Basically, you tell the prosecutor everything, everything. I didn't need to describe what might happen; that's for him or her to decide.