My husband's cousin came to visit us from America last Saturday and went home yesterday. My husband told me that she is like his big sister, as she used to look after him all the time when he was a child. She is now 30 years and my husband is 22 years when she arrived he shook her hand. And all the time she was here she kept touching him on his arms and back. Nearly every time she asked him a question she touched his arm. Then yesterday at the airport she hugged me and our friend from Yemen (who is a girl) then she hugged my husband, he didn't hug her back but he let her hug him. When I try to explain to him that it is Haram he doesn't listen, he just says she is like his older sister and there is no feelings between them. I don't know what to do. I was going to leave him for doing Haram things because his iman isn't that strong at the moment so he's started swearing and talking softly to sisters and now this. I really don't think I can take anymore. I just want to help him to stop doing what he's doing. Could you please give me some help and Hadiths so that I can tell him what Islam says about this.

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Shaking hands of alien women whether they are cousins or not is an evil. Islam does not permit it. This practice has become so common that the person who disapproves of it is considered ill intentioned and not trustworthy though the Prophet not only did not practise it but also warned the one who did so of great danger. The Prophet said: "If one of you were to be stabbed in the head with an iron needle it would be better for him than touching a woman whom he is not permitted to touch". Imam Tabrani and Bayhaqi narrated it with reliable narrators.
Aisha () said: "By Allah, the Prophet did not take any pledge except what Allah Commanded him, and his hand never touched a hand of an alien woman".
As you know, touching alien women and shaking their hands results in many bad consequences, such as arousing one's sexual desires, weakening the feelings of modesty and chastity. Women who agree to shake hands of men probably will socialize with them.
As for hugging an alien woman, no doubt it is more repulsive than shaking her hand and this is a clear sign of violating the Commands of Allah.
In fact, this practice leads to more overt sexual acts. As for justifying these acts under the pretense that there are no bad feelings and she is like a sister, etc. all these excuses have nothing to do with the rules of Shariah and the nature of human beings.
This is the fraud of Satan; a Muslim should beware of it.
Allah knows best.