Having a gut feel my BF is cheating on me!?

I've been having this feeling my BF of 7 years had been cheating on me. The reason why is we hardly have sex like I'm talking 3 times in a whole month. He tells me he loves me and everything is fine he lets me use his phone he has nothing to hide but the only thing is on weekends he will go out to bars until close I never go because I work weekends. I don't know if I should spy take is word or what I just have a feeling I don't know if  just being paranoid??