Hidden secret from my ten year old

So for my son’s whole life I’ve kept a secret from him about his biological father. The man I was with at the time took on responsibility for him while I was two months pregnant (being there the whole pregnancy and here on out). The man that is his biological father was into the streets and not a good guy. He was shot a few times and in and out of prison and I didn’t want my son around that. Recently my son came to me and said mom please don’t lie to me because I will hate you forever is that my real dad😞😞😞 at the moment I was in shock and honestly lied to my son and told him that that was his dad and why would he think something like this. I went to the man that’s been raising my son and told him what was said and he told me I’m not to tell him the truth...... what am I to do??? This is haunting me since he asked??? My son knows in his heart and I don’t want him to hate me. Advice please..... I was only 16 when I had him and I did what I thought was best. My son has a good life, attends a great school, and the only dad he knows has been great to him😟