I was sexual abuse when I was 15 what can I do

Still report it to law enforcement.  You may or may not want to go through with the charges, but tell someone so there is at least a record.  There is still value and power in "telling."
First, you can talk to someone.  As a crime victim, you will also become eligible for counseling assistance for the abuse, which it sounds like you could use.
Second, you get to take back some of what was taken from you....a sense of self and control.  Silence can be a prison.  The mere act of telling helps you break free from an emotional prision.  But....let me emphasize....tell when you are ready. 
Third, statistics tell us that if someone abuses a child once, then they will most likely have another victim at a later date.  I have prosecuted cases where a child was trying to outcry, no one would believe her, and then a relative finally stood up and said, "wait, it happened to me too...." Additionally, the evidence of one abuse event can be used as punishment evidence in the other case, should it have to go to trial.
Abuse victims live in fear that they will be looked down upon by family members or the public if they tell what happened.  In the criminal justice system, it sometimes feels like the criminals get all the protections.  This is a tough and personal decision to make.  However, by telling, you potentially open the door for someone else to have the courage to say, "it happened to me."  They can then start the process of healing too.  So, by telling someone, you aren't just helping yourself. You're helping the other victim(s) that are out their suffering in their own silence.