found out bf on tinder and texting other women!

so me and my bf have been together 2 years and im 4 months pregnant and i was on his phone (we sometimes do this with eachothers but he is usually a bit funny if i go on his) now i was texting my friend using his account on snapchat and a girl messages him and i clicked on it as i havent heard of her and to my surprise see he has been texting her for 3 months on and off and saying sexual things and saying why she on tinder and she replied looking for a relationship to which he said same!! i had no clue he had tinder and so hes been going on a dating app and adding girls to sext and act like he's single. wtf im beyond pissed! What should I do ladies cos i found out he had sexted my friend a few months ago too planning to cheat!!