Overreacting?

So my boyfriend and I just found out that I’m pregnant 2 weeks ago. I picked up his phone and in his Snapchat memories, I found a sex video of him and another girl(from before we met). It’s bothered me to the point I’m not sure I can get over it. I don’t know if I’m shutting down this way because of pregnancy horomones or if I should really be this bothered. Its to the point of me being so disgusted that I’m wanting to leave him. Any thoughts??