Ah I can't even how imagine how horrible that must feel
I guess the only thing I can say is try not to beat yourself up over it... there was no way you could have known he would actually end his life when you didn't call... maybe the call wouldn't have even made the difference, who knows? I know this probably doesn't help much and I'm sorry, I wish there was something more I could do
It's beautiful that you got a tattoo for him and although you will probably always feel the pain of this, try your hardest to remember the good times and reach out to people, like his family, especially with his birthday coming up. It's great that you are seeking help and really try to remember that it's not your fault.
I hope you feel 100X better and pm
me if you want to