Stay or Leave? at a total lost 😕

Me and my bf have been together almost 5 years. We have a son together. About a month ago I caught him sexting a girl that is only 20. He is almost 39. He told her she was beautiful and sexy and he loves her. I confronted him about it and he said he put an end to it, but i dont think he did. He keeps hiding his phone when i walk into the room and says it was an email or one of his friends. He deletes everything so theres  no way of checking anymore.  I'm beyond lost on what to do anymore....