You can proceed with your assault charges but you need evidence. Anyone can say anything but people who win in court, provide admissible evidence.That is, evidence pertaining to the case.
You will need witnesses. People who saw your bruises even if they did not see the attack and have them testify about how upsetting this was to you at the time. Bring in pictures of the bruises. Get them blown up to 8x10, if you can. And, of course any eye witnesses to the attack.
Also, have the police reports from the times you called them.
If you can show that you have evidence from reliable sources, then you may be able to get the charges to stick.
So, you went back to him for more abuse. That in itself shows the mentality of a battered girlfriend and may even be a fact in your favor.
Most battered women go back to the abuser.
If you can, see a counselor about being an abused victim. Bring the report to court with you.
If you really want to nail this sucker's butt to the warrant bench, you have to prove your case. It is up to you and only you. good luck