My therapist has told me that it's pretty impossible to go from an intimate relationship to friendship straight away. There are too many emotions involved and one if not both is bound to get hurt. He suggests that the only way is to cut all ties for a couple of months and then if the friendship is meant to be then get in contact and see what happens.
I know this doesn't help your situation and I feel for you but if he is in love with you then you are not the person that can be there for him as the mixed feelings will only hurt him more (my opinion from experience). You can't give him false hope that you will change your mind (once again personal ecperience)
I wish you luck