He's losing interest in me.

Alright ladies: first and foremost, I snooped and I shouldn't have.. because we all know what happens when we put our noses in places they shouldn't be. 
I found "Losing interest in my girlfriend" in my boyfriends browser history. Now, yes this hurts like a BITCH.. but I can't say that the feeling isn't mutual. We've been together for going on 3 years now and have been into each other since we were basically children. We live together in our own house and we have a dog together.. but I can't help feeling like our relationship is running its course. 
I'm very torn because I know I love him but I just don't think that we're in love anymore. It's sad, I love his family, his family loves me. We also dropped a lot of money to go to a concert together in June ($400//Person). I don't know what to do guys.