There is no answer here for you. You are a victim of domestic violence and you are very very pregnant. That makes things worse for your boyfriend. Perhaps his bond can be reduced. If there are pictures, you were ore than "slapped." Reduction and release will be up to the judge. Not you are making excuses for him by claiming it was your fault. You need counseling as badly as he does and I hope you are able to get it. It is a sad situation for both of you as well as for your unborn child.
It is very unlikely his bond will be reduced, absent new information. If he wants to get out, he needs to get his family and friends to foot the bond. Furthermore, hearing you say that it was your fault that he hit you is extremely worrisome. I recommend that you seek immediate counseling and find a new boyfriend asap. I've attached a link to a local organization for help.
Self defense is allowable in Domestic Charges. I have tried hundreds of domestic cases where there is a finding of not guilty when the victim is a women and the defendant a man. It comes down to you testifying that you were the initial aggressor. You need to insist to your public defender that you were the aggressor and as you said "provoked him to hit" you. Even if there are pictures, if he reasonably believed you were about to attack him he may, in some situations, strike first. If the prosecution will not drop the charges you must remember that you are under no obligation to cooperate with them, if they subpoena you then you will have to come to court and testify, but it is your choice to talk to them before the court appearance, or even in court prior to your testimony. I suggest you go directly to your boyfriend's lawyer.
I do note, that staying with a person who hits you just because of the financial hardship of not being with that person does not sound either healthy, or like a good idea.