"She steals someone's husband." that is a sentence to start gossip. The truth is your partner who loves you can't be stolen. He is not a hostage, he has own choice and will. If he decides that he is not comfortable with you, that he doesn't feel happy, he will focus on another woman.
We give and receive signals from our souls. If you are not alone, but you feel emptiness, something is missing.
Paul got married to a woman who was in a relationship with him 2 years ago. She was young, pretty and rich. He should be happy because his life was comfortable, he did not have to work his hard job as a waiter. Many doors opened to him. He felt something is missing, he said that he respects her, but love is somewhere else. Sparks were not in the air when he was with her. She was attractive, but he froze around her like in the Ice age. He met Adele, she was older than him but in her presence, he felt hot. When she smiled his voice melted. Even Adele was hot-tempered and blunt, Paul could not take eyes off her.
Chemistry can't explain why we are attracted to some people, and why others leave us indifferent. One thing is sure, the partner can't be stolen and the other woman is not guilty if your man runs toward her. The third person comes in the relationship that was full of holes already. When you can't find something in your relationship you will start to ask it somewhere else. Your energy will connect with someone else's similar energy and your old relationship will fade.
What kind of emptiness can be in one relationship?
Lack of support.
Underestimation and humiliation.
Some relationships are too tight and partner needs more freedom. Another type of relationship can be too weak, in the way that one of partner loses interests and another half is feeling alone. So, when the end comes, it was never overnight. It happened a long time ago, just you did not notice it before.