How to tell your child daddy killed himself

This summer my 8 year old's father committed suicide by drug overdose. My son was in Disney at the time w/my parents so my husband & I had a week to decide what & how to tell him the news. I chose to tell him the truth about the overdose & drugs but led him to believe it was accidental. It's been a few months now and we're beginning to see some red flags in his behavior that have me very concerned. He's angry with me for leaving his father 5 years ago & for not making his dad stop drugs. I think he knows, or at least has a hunch that this was no accident & thinks I'm lying to him. He has outright asked me if daddy did it on purpose but it breaks my heart to think of telling him the whole truth, that his dad chose to leave him without his father. Would do anything to take this pain from him. Would he be better off knowing the whole truth?