Giving you the benefit of the doubt...
You're 14, your body is still growing up, hormones raging. What you are feeling and going through is completely natural and to be expected.
It is natural to be attracted to other girls and natural to have "thoughts" about them. The key is whether or not you act upon those feelings. If you can control yourself, it is a sign of growing up and maturity.
As to whether you love her - thats a harder question to answer. Certainly the odds are stacked against you, but that should hardly stop you. You guys have been together for a year, which is quite an accomplishment. You should consider, however, (as has been said above), whether you truly love HER, or if you love the sex you are getting. If you guys stopped having sex for 6 months, would your relationship survive that?
One last thing - use protection - having fun is one thing, ruining your life is entirely another.