In this day and age, you have to shift your mental foundation and build around some fundamental rules.
Here are some key fundamentals every man needs to know
1) You have never owned her vagina and never will
A lot of problems men have is centered around thinking they can do something to own her vagina. This is how a lot of simping behavior starts. They get in the mindset of, "Well if I don't do this or that, then another man will." But as you can see in this day and age, the guys that do everything for a woman are still getting cheated on. "Doing things" for your woman will not get her to keep her legs closed. Also, as much as a woman tells you her goodies between her legs is yours, as soon as she leaves, it's going with her. The importance of realizing this rule is that it will eliminate a lot of undesirable behavior on your part. If you know you can't ever own it, you won't engage in actions that you think are necessary for you to 'own it.' A broad tells you to lick her toes, and the average simp guy will end up with toe jam all in his teeth because he will be under the impression, "If I don't do it, some other man will." You only ever rent it, so stop doing all of these unnecessary things in order to try to 'own' it. If she wants to give it to someone else when you're not around, that's exactly what she will do and there's nothing you can do about it.
2) It's behavior, not labels that matter
This is something every man needs to drill through their head. A lot of guys think they 'won' when they are in a 'relationship' with some pretty female, but that label doesn't mean a doggone thing if it isn't backed by the right behavior. If she's doing more for ANOTHER guy than she is for you and yet you are the one in a relationship with her, what do you really have? This isn't to say don't get in relationships. It's more along the lines of don't just accept 'being in a relationship' with a woman. Make sure she has proper behavior and respects you and you are gaining exclusively positive behavior from her since you will be taking on additional responsibilities and risks that a relationship entails.
3) Never, ever get too caught up
In this day and age, we've had the countless stories of what people are capable of. No matter how sweet you think the woman you are with is, NEVER put anything above her. You just have to be mentally prepared to walk-out if she is doing something foul and to avoid putting yourself into disadvantageous situations during your dealings with women. You don't want to be one of those guys, who upon finding your woman wasn't loyal, goes crazy and hurts himself or does something that gets himself locked in prison for the rest of his life. Keep your heart in your chest.
4) You can't convince a broad to be loyal
Guys get this impression that if they 'do the right things', that a woman will be loyal to them. Not going to happen. Loyalty is an internal character trait. If someone has snakish characteristics, that's just who they are. Women get caught up with this a lot of times as well. They go for this playa type dude and think that THEY have the magic box and skills to make this negro loyal where all the other women failed, and they soon find that a wandering mind stays wandering. You need to look at the woman's CHARACTER and see if she has demonstrated loyalty before getting exclusive with her.
I said all I've been saying to make this point. Don't make your decisions based upon 'keeping a woman around, trying to win her over, or trying to please her.' Make your decisions based off what you feel a man would do and how he should maintain his respect.