You need to make love to her in a way that blows her mind. You need to Bleep her so good that you are the only man she wants to have se x with. You need to have a se xual connection with her that will guarantee that she would have no need to think or fantasize about another man.

Sex tip
There are no guarantees in life, but when it comes to keeping your woman happy, there are a few things that makes it less likely that she would stray.

Pleasing women is not simply about the sex part, it is making sure you reach her emotionally too. If you do not do that, she might go find that emotional connection elsewhere. And you know that when another man begins to bond with your woman that way, it is only a matter of time before he has her in his bed.
You need to make love to her in a way that blows her mind. You need to fu ck her so good that you are the only man she wants to have sex with. You need to have a sex ual connection with her that will guarantee that she would have no need to think or fantasize about another man.

To do this, it all comes down to making her feel good. Here are 3 ways you can achieve this.
1. Compliment: When in bed, she is n aked and vulnerable, never underestimate how far compliments can get you. Tell her she is beautiful and sexy. Don't just say it, make her believe it. Tell her why you love parts of her body. Unleash the se x kitten within her with words. Do not make her have even a second of doubt about her body. If you do this right, she would look forward to being with you, not just for the s ex, but for the way she feels during it.

2. Be selfless: Most men claim they are a selfless lover but sometimes this is untrue. How do you define selfless, is it just when you have pre-intimacy or try to make her cum first? That is not what being selfless is about. pre-intimacy is a necessity, and always pushing until she cums first will only put her under pressure. Selflessness is making her feel whatever she wants is okay. Take time to actually know what she likes. Do not just assume because other women like it, she would too. Make the effort to know who she is sexually, and go from there.

source and more : http://spicyblogz..com/2016/01/how-to-make-sure-you-are-only-man-she.html