When do I tell ?

Ci

Hey ladies a bit of a back story, I had my first born in 2011, me and his biological father had a rough relationship and I left raised this boy on my own, I met my love of my life and he met another, we both had babies to them so my son has a half sister out there, that year I find out he committed suicide and yeah. He wasn't around for our son at most he maybe spent like 2 months in his life, it took him a whole month to even meet him when he was born. What I'm asking Is how do I tell my boy that he has a half sister and do I say his biological dad committed suicide when he was 2 or ?? he's nearly 7 by the way, I just don't know how I'm going to do it...