go ahead and tell her... what's the use of being together if you don't open up to her of how u feel... it's all a matter of how u say it bro... then she wud feel flattered or find ur jealousy sweet hehehe... but don't nourish this feeling too much or else it will get out of hand and this will add flames to ur growing insecurity later on and this could get ugly.
be happy for her, support her coz she draws strength from u as her bf... just come to think of it, the other guys can ogle at her and pine for her but at the end of the day, u can do so much more coz u have her
so stay cool