I'm about to freak out

I found a condom in my house and my bf and I don't use condoms never have. I have a roomate but I can't imagine him leaving it anywhere but his room. My bf and I have been together 10 years and I'm 18 weeks pregnant with a baby we planned. I'm trying to think the worst but really what else can I think right now? Why do u have a fucking condom! He's at work right now so when he gets home I'm calmly going to tell him that if he's having sex with someone else then he needs to tell me right now. If he says he's not I'm gonna be like well then why do u have a condom!!! Seriously I'm trying not to get super upset right now but it's almost impossible.