When a person is very depressed like this, you should not take his loss of feelings for you as anything but his loss of feelings for life, for himeself, for his future. It is a very serious matter. YOu will not be able to rescue him by love or devotion, but he can definetly get help from a professional, and I would encourage you to encourage him to get help immediately, if possible. YOu may not be able to do anything more than recommend it. You should also be prepared for him to reject your recommendation, but at least you will have done all you can.