I Like Another Girl!!!!?

Me and my girlfriend have been going out for almost 3 years, but recently we've grown distant arguing over literally nothing and we just fall out all the time. I have since become slightly infatuated with another girl and she likes me as well, now we have some theories like because we are best mates our minds have gone slightly overboard and thought whoa you like this girl now, and i also think because me and my girlfriend are going through a 'rough patch' as such then that's why i like her. But this other girl, we have the same interests in music, hobbies and we just seem to connect. But this other girl wants me, but she also has a great friendship with my girlfriend and doesnt want to ruin that. Please someone help me.