So 2 nights ago

I went to get on my fiancés phone to watch Netflix because he told me to start our show and an email from lady pops up she was asking about sex! They had 187 messages and a couple pictures between each other about sex and meeting up! Even better he was pretending to be me talking to other ladies to hook up for sex! I'm 10 weeks pregnant with his kid and I'm his fiancé what do I do leave or stay act like I never saw it? Oh also he did this with 3 different ladies! :( but has never met up with them?