Help with me and my problems (not pertaining to my name)

Hi there guys. Recently, my girlfriend (17 years old) and I (17 years old) have been experiencing a period in our relationship that isn't the best. We haven't had many downs before, so this is an odd situation. I have been with my girlfriend for around 1.5 years now and things are getting pretty stagnant and boring for both of us. Before, there was attraction, much caring, and a lot of fun. Now, we aren't really clicking like before and we have been looking to other people (the both of us). For some time (even before I started dating my current girl), I have had feelings for a friend of mine (17 years old) and often flirted with her between classes (I'm a junior in highschool). Recently as things have died down between my girlfriend and I, my eye has started to shift to the other girl. I'm not happy about this, seeing as I still have strong feelings for my girlfriend, but at the same time feel as is we are not as happy as we could be. I don't want to leave her, but I feel like my attraction to the other girl is strong enough to do so. Any help that you could provide me is great, and I'll be sure to answer back. Thanks guys, it means a lot.