Advice :/

So me and my bf broke up around a year and a half ago. After we got back together 5 months later, I found out he had been talking to someone. It’s been this long and I still find myself thinking about what happened. To make matters worse, I always have the urge to stalk through that girls social media but I don’t know why. I really want to move past it since now we’re almost four years together and it’s been almost two years since it happened. Any advice?