I really need some advice on my relationships

I like a guy (let's call him Dave). He knows about it & he likes me too. We just found out his best friend (aka Sean) is infatuated with me. Sean doesn't know that Dave & me like each other. Sean is desperately trying to date me but i've told him many times that i like someone else & he's only my friend, nothing more than that. Since last few days, Dave hasn't been talking or texting me. I found out from a mutual friend that Dave is backing off for Sean, even though he likes me. What should i do? I don't want to hurt Sean's feeling & i want Dave to understand.