What do i do?

Lately ive been seeing my SO texting other women. One i know is from work. He never used to text other women that much. Idc that he does because im used to him having to deal with his ex that he has a kid with. The thing im uneasy about is i dont who these women are and he usually tells me and i know most of the women in life as we have been together for 6 years. He made a big deal about my friend(a guy)texting me so i stopped talking to that friend out of respect for him. My SO didnt like the way we talked because we were close and he felt uneasy about it. How do i go about asking about these women that he is texting because i dont want to come off assuming anything but this is unlike him. When he gets texts from them i see the name and he texts back quickly and his hands are in the way so i dont see much else so i dont know what is being said. I might be over thinking it but i guess im worried because we have been having a few issues lately so my mind may be thinking the worst.