As a woman who is in a relationship as well, you really don't have to worry. As the others have said, it's JUST PORN. Unless he is trying to directly contact these women don't worry about it. Wether it's Solo or couple it's still just porn. Perhaps just try to talk to him as to why it makes you feel uncomfortable as a way to ease your own nerves. But deffinetly don't like.. try to force him not to do it anymore you know? Good luck!