My son misses his daddy...

My kids father and I broke up because of him cheating. We were coparenting okay but then he randomly stopped seeing thw kids. And we have a baby together too. My sister sent me a video if my ex live on Instagram having a full on mental break down. Like slicing his arm on camera and talking about being raped as a kid. Putting a gun in his mouth and pulling the trigger half way... I called the police to do a wellness check on him and hes been admitted to a mental institution. I'm not sure how long he will be there. Ive been keeping up on updates with his mom. He's on mood stabilizers and they believe he may have been dissociating during that break down. My son has been asking about daddy and he misses daddy. I really dont know what to tell him in a way he will understand... He's very sad about everything and doesn't understand why daddy hasn't come to see him..