Thank you for your concern
Your concern for your friend is genuine. But remember one thing. No one can be responsible for any one's suicide
. You can be just be an excuse. Its that person's own fault. So you don't have to worry about feeling guilty. At the same time i understand that it is not easy letting a friend go. But for your own sake it is important, so it is for your friend too. Try gradual. To begin with try ignoring one call a day. Initially call him in 5 min and apologize, giving him a good excuse like you were driving or in the rest room or so. Initially increase the time in which you call back. Then stop calling back a few times. When you are with him try not to say much. Listen but don't participate. Let him feel its not going anywhere. Yes but do listen intently. Your friend needs ears. Lend him. Establish your boundaries. Don't encourage too many plans when you two do things alone. Instead involve him in group activities. Help him interact more with others too. This way you help him get independent of you and you get rid of your burden too. In a while target changing rooms.
Hope that helps
God bless you