There is a saying "butterflies in my stomach(belly)". It is usually used when you are deeply in love with somebody and anytime they look at you or talk to you, you could feel a little tickle in your stomach that moves around. So the full sentence "you can be the butterflies I feel in my belly" could mean "You could be the person I fall deeply in love with". I haven't ever heard the sentence said like that before, but my answer would be what I assume they would be saying. Hope this helps.

In English we say you give me butterflies, is this what you are meaning? This saying means you make me nervous, happy, and excited. Hope this helps.