Can you please help me with friend and man problem??

Your friend may be jealous of him and worried that he's going to take time away from her. That's mostly what goes on in these type of relationships. My advice, just give it a shot with Dave and if it works it works, if it doesn't then whatever. It's not the end of the world. if Sue doesn't want to be your friend because of it, then screw it... she's not that good a friend then.