We all go through less 'serious' stages of dating in our lives where we are seeing more than one woman... these can be temporary before any relationship develops into something more important when you're playing the field, or just a way of life for you. If you think about it, you'll also realize that many men attract a lot of drama and disruption into their lives when they are dating multiple women and it goes wrong. Affairs and getting caught cheating. Friends with benefits that want more. Women getting upset with you in general. One of the keys to eliminating all of this trouble when you're dating more than one girl is 'discretion'.You never talk about the fact that you have multiple girls in your life. You don't talk about it to guy friends - nor to girl friends. You make sure the girls you are seeing know that. For her to stay in the relationship you have, to not get hurt or angry, discretion is essential. She has to feel safe, and discretion makes her reputation safe. You let her know this by:
1) Acting discreetly. Actions speak louder than words - if she hears you being in-discrete about something else in your life, she is going to assume you do the same with your relationship.
2) Letting her know you act discreetly. By subtly indicating you value discretion about subjects in general when the subject is relevant. For example when she asks you about something you're being discreet about say "I don't want people going around knowing my business."