I Can't Do The Impossible!

Ok so let me start by telling you some history, I have this friend, he has been my best friend for 11 years and he is Indian and kinda chubby and I have helped a lot of people with their relationships and getting girlfriends and boyfriends and so on. So he thinks I can help him with this one girl and he has complete faith in me getting this girl for him, but I accidentally in the process of trying to help him and talk him up to this girl she started liking me instead :( So I definitely don't want her I am not that sort of guy I mean she is nice, smart and funny but I couldn't do that ever. So now she likes me and he thinks that I can get her to like him when she just wants to be friends and he just doesn't understand, she has let him down easily and I have tried to be really nice about it but he wont give up. She thinks she is out of his league and to be fair to her he is very immature and naive but still! I can't believe this is happening! he is my best friend and I cannot just tell him I have tried but he doesn't understand and he is now thinking of asking her out when I know she doesn't like him, and that will devastate him. I just want everyone to be happy but I can't seem to find a solution and when I asked him "Maybe she doesn't like you, Could you just stay friends?" he replied "I've got to make her interested" and when I asked him "How are you going to do that?" he said "That's where you come in!". I simply don't know how to figure it out should I just tell him to move on again for the thousandth time I know this isn't a big problem or anything just if someone thinks they have the answer I would appreciate it a lot, there is no chance for him and the weird thing is he is arrogant and thinks he is attractive when that's definitely not the right attitude to get any girl and I can't help but think that I am a bad friend and none of it's even my fault lol just because I have helped others get relationships doesn't mean I can help everyone I just wish there was some way to tell him that going for a genuine girl is a better idea instead of a 'popular hot girl' but boys will be boys!