What would you do if your boyfriend's best friend came up to you and said he has strong feeling for you and you two are good friends

I'd say, "Sorry. I'm taken."

Tell him that he should be ashamed of his self for talking like that to his best friends girlfriend. Also to be honest you should tell your boyfriend, this guy is no best friend, if he goes after his girl.

I would tell him you don't appreciate that and he is inappropriate and if he says anything else to you, you will tell your boyfriend.

I would ask him if he thinks it's okay to go after his best friends girl, and ask how he'd feel if it was done to him.

Bottom line, just because he has feelings for you, doesn't mean you have to honor those feelings. Tell him point blank that you considered him a friend, and that you're shocked that a friend of yours, and your boyfriends, would put you in this position. That's not how a friend behaves.