I'm scared of cheating - Please read - 22 year old male?

I ask that you read this fully to understand my position firstly.

I fully love my girlfriend, we've been going out for almost three years now (August 8th) and I genuinely see this as the girl I want to spend the rest of my days with. I dont know how to show this online, but I pretty much think about her and being together on an hourly basis. Even on the train ride home today little things like seeing houses would make me think about living with her in a house together. Even a field I went past I thought about being in it with her and being free. I love this girl more than ever and I'm unbelievably happy with her. Not to play the 'good boyfriend card' but even two months ago, the night before her final year exams was also the night before my job interview for the first ever paid job I've had - And she was feeling ill so I travelled to her home (2 hours away) and looked after her the night and made sure she had a good breakfast etc before she had her exam - and in turn missing my job interview. Again - I'm saying this just before anyone goes "you're just a guy" "you're don't love her".

I worry as I'll still get attracted to other girls physically say if I seen them in public (I've never had feelings for a girl while with her, not even a slight crush!) every now and again, and I worry that in the future if one of them ever made a move on me, that if I was horny I might give in as I'm 22 now and we've dated pretty much since I was 18, so I've no experience with girls really