Should I be worried

My boyfriend and I have been together for 3.5 years, and the last year or so our sex life and anything exciting in the bedroom has really started to dwindle.

I had all my family over for my birthday this weekend, including my boyfriend, I had a great night and really got to enjoy myself spending time with my cousin and my boyfriend.

However, I was looking for something specific on my boyfriends phone the day after (I had permission to look on his phone) and I came across some texts between his best friend and him, talking about how hot my cousin is and how he would love to get up in there. Should this be something I should confront him about? Or should I just let it be. I’m so undecided