Ya i agree to let him know.. at least u try.. if u never try u never know maybe it end up great. If really he rejected then jus treat it as an experience at least u can tell urself u got an answer and not unknown for the whole life.
you should not go for him you should also talk to your friend, let her have him, but let your friend be aware so they can be more careful around you (not so much PDA around you to hurt your feelings)
think about it, you already know the answer .... wouldnt it be stupid to go after a guy that doesnt like you ?
agree make it happen besides a lot of the time a lot of people get along and then when one asks the other hand even if u get rejected they can persuade them to go out with u. patience and perserverance pays off sometimes. do what that guy does in the notebook lol.
If it were me, I'd ask him if he liked my friend. If so, I would step aside, if not, I'd express my feelings for him.
Some guys act differently towards the girl they like, sometimes rather than being nice to them they try to show minimal interest in them. Just give it a shot, but it be better to ask if he likes your friend first.