Hello Guest_0846, for you having to experience this must be heartbreaking and I am so sorry for the loss of your best friend, especially as a group was supposed to be looking after him.
Unfortunately, there are three issues you need to decide on, to cope with your loss which is going to be so difficult, or to approach the group to see why this actually happened, and thirdly for you to get some assistance from your doctor.
There will be many questions you will keep asking yourself, but you may not have the answers you were expecting, but your GP can refer you to a psychologist and also offer some helpful sites for you to have a chat with.
If you could open up and let us know a little more, then we can help you even more but please look after yourself.
Take care.
Geoff.