I think im falling out of love with my girlfriend?

HI im Joel and im 16, ive been going out with my girlfriend for about 10 months now, and everything is not as lovely and amazing as it used to be. Wed been best friends before we went out, and she dumped her previous boyfriend to go out with me. Things were perfect, and whenever i saw her my heart would literally ache because i loved her so incredibly much. We have exactly the same sense of humour and im round her house like 3 times a week. Im really friendly with her family although they are split up, i get on really well with them. We were so in love after about 5 months that we told each other wed be together forever, we really meant it. After about 7 months we became more ually active however we have not had . I know its really bad, but ive fancied a few girls lately, however i 'think' i still love my girfriend too much to break up with her. She loves me the same amount as she did since the day we got together. She texts me so much, we still have really nice moments. We laugh with each other so much, and have alot of fun when were together. However i dont have the same exhilerating feeling i once had with her. It really saddens me :(. However when i think of life without her, it feels bad because i like her mates and her family alot and me and my girlfriend have shared really nice romantic and perfect moments together, id hate to ruin that :( . Ive tried going to the places where we once went when we first went out and ive played the songs i listened to when i was powerfully in love with her. Id hate to break my girls heart, she is so good to me, but im not sure if i still love her, or if im just going out with her to keep her happy. Im really upset about this, please help me out it would be really appreciated :( .