It appears that your boyfriend has been charged with criminal sexual contact with a minor, under the assumption that you were only 15 at the time. In most States, the age of consent is 16, meaning that had you two engaged in this sexual activity, or presumed sexual activity, he most likely would not have been charged.
If you were subpoenaed to testify against him at his preliminary examination, you will have the opportunity to speak with the D.A./prosecutor and explain the details of what happened and that during this entire time you were 16 when this conduct happened. The prosecutors could consider dismissing the charges, but this will be within their discretion to do so.
Be mindful the age of consent varies with each state, and the consent factor does not come into play if your boyfriend was a educator, administrator, or acted as a teacher within the State. If these factors exist, he can still be charged despite you being 16.