Well, for the sake of this topic, I'm gonna be serious.
ONE: Stick to your own rules of your life. You are the king. You do whatever you like. You say whatever you like no matter what. Nobody tells to do that and to not do that.
TWO: Ask yourself. Are you looking for true love, a girlfriend who you and her each devotes to the other for the sake of loving each other? OR are you just ladies-man? Don't ruin someone's else life if you can't suppress your lust of women.
In case you have a girlfriend or what appears to be a shallow relationship. You need to be honest with yourself and the girl.
Personally, I despise lies. So I'm gonna tell you not to lie to anyone, and specially YOU. Don't think you're the man among men and hotshot. Trust and respect are important in relationship. You can be friend with other girls depends on situations. It doesn't mean you're gonna cheat on her. Just when you get back home grab her, hug her and kiss her. That helps to keep you emotionally away from other girls.
Seriously, some girls plan/like to ruin relationships of others for their own pleasures.
If I have a girlfriend, whenever I come back from work or any place, I would directly hug her, kiss her and tell her how much I love her. I see many women, and I get dirty/perverted thoughts. This and I'm single. I can't restrain my lust for women.
However, having a girlfriend, she can't tell me what to do and what to say. If she doesn't like my way and if she doesn't trust me, she can leave me and I'm all fine. At least not to hurt her. Cheating is harsh. Being single and spending nights here and there and getting laid with different girls, life isn't about that. Welcome to the nastiness of this world.