You can make a withdrawal statement.
However, you should be aware that the Crown Prosecution Service (CPS) now has a policy of pursuing a Domestic Violence (DV) offence even if the alleged victim has subsequently withdrawn their allegation. They have a number of ways of doing this and one of them is to issue a witness summons to you to compel you to attend court to give evidence. Although they are not generally in the business of prosecuting victims they may also charge you with wasting police time.
The reason they have adopted this policy is because the number of DV victims making statements and later withdrawing their allegations has almost reached epidemic proportions. A huge amount of time is wasted by the police, the CPS and the courts in dealing with such matters.
You might also like to be made aware that those who dish out domestic violence rarely “get better”. On the contrary, if left unaddressed, they invariably get worse and you may find yourself on the receiving end of some really shocking violence. If you feel physically sick now you are very likely to feel a whole lot worse after the next "session".
You would be advised by many people whose business it is to pick up the pieces after DV that the best thing you can do is see the matter through to a conclusion. Your boyfriend may even thank you for it in the long run but if it means losing him it may be a small price to pay because quite frankly, anybody who knocks you about even once does not deserve your affection.