How do I recover from the death of my bestfriend?

Also a TW for suicide?? My best friend died of a heroin overdose 2 weeks ago. I wasn’t there when they found him but his mum called me that night and I am now staying with her (I’ve lived a state away for a year, I drove back when they called me and I haven’t gone home since) I’m a wreck. I can hardly sleep or eat, all I do is take care of the house and his mum, she’s worse off than me of course. But I don’t have anyone to turn to and certainly not anyone back home and I’m scared I’ll relapse if I go like this for any longer. My mate was my only real support and i dont even trust that he didnt OD on purpose and if he couldn’t survive life I don’t know how I will. I need to hear what got other people out of this. I know I’m just grieving but how do people survive this kind of grief.