Did I cross a line?

Was I crossing the line? My son was receiving a call on Facebook through my fiancés account on the iPad. So I picked up the iPad cause he wanted to call my son again so I searched my sister in laws name and saw in my fiancés search history was his ex fiancé. he asked what’s been wrong and today I finally came clean and said I saw what he’s been searching. He instantly got angry and began yelling. He complains about not being able to hold a conversation with me but he’s the one who gets right angry and I can’t even talk. Now I’m the bad guy and I’m sure he’s going to bring his mom into this to yell at me also. I’m so sad we have three children together and have been through a lot of hurt both ways already. I thought this year was going so amazingly until now. What do I do??