"marry my sister"

John and Thomas were first year students.One day they had some diazepam for fun. It is euphoric and can give a relaxing effect. They were having a very nice time.
They might have taken those tablets around 5 pm and when the night came, there was a booze party in the hostel which was compulsory for all. All kinds of drinks will be poured into a big bucket and will be mixed with water. A mug will be kept inside.After boozing, both of them were having a chat with a senior.
During the conversation the story of the diazepam came out.
"Jesus, you had diazepam before the drink?"senior asked.
"Yes..why.....is there any problem..? "
"How much you had..?"
"I had only one but he had ten, I think...!"
John pointed his finger towards Thomas.
"Then he is going to die. If you take diazepam and alcohol together, you will die. And if you don't die, you will go into coma, that is sure. There are hundreds of people in coma in the United States..."the senior continued.
Thomas felt like the earth is sliding away from his feet. He actually had taken fifteen or more and he kept that secret hidden from everyone. He took john with him. They went to the terrace. John was also bit afraid but he had only taken one diazepam and that gave him the benefit of doubt.
Thomas started crying like a child.
"I have a sister and a mother. You already know that my father is no more..! You should take care of them..You can marry my sister..."
He told John.
John too was very emotional. He agreed outright. He had to help his friend in this situation.
In the following morning John was awakened by Thomas.John felt very happy.
But Thomas said,"don't think that you can marry my sister."
"Why?"
"Do you think anybody will put their hands on a snake's mouth?"
NB:Both of them never took diazepam again in their life!Sadly, Thomas had died a couple of years back. He also died of a heart attack like his father.
Both of them died around the age of 35!
John is still alive. The memories about Thomas still haunts him. They were very good friends throughout their life in the college.