My mate has a bf but she fancys another guy.i like him too but sud i feel bad 4 likin him? knwin she likes him

she liked him at the start of college but nothin happened so now she's got a bf. Recently me n him have bin heavy flirtin on msn yesterday we went out on a date so the cinema. i dunno whether to tell my mate. Coz i know she likes him too and she mite say to me "u knew i liked him" . i dont wanna lose her as a mate but i do like him. im really confused.