Some girls don't think men who chase women are cool. But as long as a boy or man isn't getting too much on their nerves, most girls and young women feel flattered if a man chases them.
You can go all out to show interest. If you do so, you'll have a chance to land her in bed even if from the beginning, she didn't contemplate you as a sexual partner. She may even be in a steady relationship with,or married to, another man whom she loves. What sweet illusion!
You want to have a lasting impact. Teach them a lesson. Destroy their marriage.
She may steadily refuse you... for how long? Go all out. Tell her she's the most beautiful woman you have ever met. Tell her she's the woman of your dreams. Demand that she divorce. Tell her that you will marry her. You haven't slept with her yet. Never mind. Tell her that you will be faithful with her until the end of your days. Tell her that if she doesn't grant you a night together, you will never again touch a woman. Promise her anything you think she would like... or rather: like to hear. Don't worry, you don't have to keep any of your promises. She won't believe them either. It's just that they sound so nice. She'll like to hear them, but she won't believe them. Or, after a while, she believes them a little bit. They just sound so nice.
If you have time, wait for her. Wait for her when she leaves her school or work place. You don't have to talk to her if it would be embarrassing for her. Just make sure that she sees you. Give her the feeling that you are really, really interested in her. But keep an ironical twist to it. Promise her so much that she impossibly can believe that you are serious. It's a charming game. Smile while playing it.
You'll have your day, I guarantee it. You have a great advantage over her husband. They live together. You just meet her when you plan for it.
Their living together won't always be harmonious. Sometimes they will argue, and sometimes she will be disappointed with him. She even may sometimes desire sexual intercourse when he is not in the mood, or when he is busy with his work. Sorry, my Darling.
Watch out for the days before her menstruation. You'll have your chance. She will grant it to you, at least once. And if you can give her a good time, she'll be back for more.
And then, go all out for victory. Make sure her husband will learn about it. Fuck up their marriage. Why? Because marriage as an institution is a disease. It can never be what it is pretended to be. If anything, it can be a depository of losers, of men and women who can't have what they want, so they take what they can get.
In spite of all your promises, you won't be foolish enough to replace the idiot she has been with until she met you. You'll leave her at a time when it will still hurt her, not you.