My son knew he had an STD and didnt tell me...does he not trust me?

He is 15 and I forced up to break up with his 21 year old girlfriend after I learned that their relationship became ual and told that girl to stay away from him unless she wanted to be charged with statutory . He was grieving for quite some time, but he got over most of it after I got him into therapy. We went for a checkup earlier in December, and the doctor called me to let me know that his blood tested positive for syphilis. I confronted my son about it and he said that he knew about it all along but didn't want to tell me. I feel crushed. Does he not trust me anymore? AND YES, we are getting antibiotics and it is curable (thank God), but I can't believe he would hide something like this from me. Does he not trust me anymore? How could he do this to me?