romantic relationship problems

im in a relationship with someone. shes so sweet and absolutely lovable but i always tend to feel like we arent “made” for each other. sometimes, i cant help but feel those goofy butterflies but sometimes, they go away. theyre just gone, and that scares me. im scared if my feelings for her arent real, and if they arent, i dont know how to approach her. im afraid of breaking her heart.