Relationships idk

So I've been dating my bf for about 8 months now and I've been trusting him. But Lately I've seen him snapchat this girl that has been posted as his "WCW" two years ago and he definitely has had a thing with her.  He likes all of her pictures on Instagram and Facebook as well. I'm not sure to be worried about it? I feel like I'm overthinking. But loyalty is rare nowadays.