I like this older girl?

So I'm 15 and this girl is 18 and I've know her for almost a year alreadyy and I really like her but I don't think she knows or have notice that I do and I don't really want to tell her bcuz I'm afraid it would change the way she looks at me and me and her are like "wifey and hubby" and we hug alot and when we walk I would put my arm on her shoulder and she puts it around my waist. She's the only girl I ever think about and care about. Idk what to do anymoree sometimee I wish I was her boyfriends but the only close thing I got right now is being her hubby... Thanks for taking your time reading thiss