Grieving my sister's ex boyfriend

[LagataC99]

Back story:

My sister dated this guy for about 5 years. He lived with us for a short period of time until he bought a house. He was good to my sister in the beginning of their relationship, but he then cheated on her several times, which ultimately led to the relationship ending. He was a partier in his early-mid 20s when they were together. I didn't think much of him, as they ended their relationship about 9 years ago, until my sister told me that his family reached out to her to let her know that they were taking him off of life support the other night. Apparently, he had liver failure due to cirrhosis, I'm assuming from drinking and also it seems he did not have another relationship since things ended with my sister 9 years ago. He was 36. 

In 2018 at the age of 32, I was diagnosed with a rare aggressive cancer. By the grace of God, I have been in remission since July 2019. *This part may or may not be important*

I have not talked to this guy in 9 years, but for some reason, I am grieving him hard. I keep wondering - why and how. How did he die from liver failure at 36 when there are people who drink for years and years and don't get cirrhosis until later in life. Why... why did he make poor choices? He knew that he had a liver issue and had some hospital admissions from complications related to the liver issue but continued to drink. If he knew he was sick, why didn't he stop? I know I'll never know these answers and I work in healthcare so I know that 1- people make poor choices, 2- addiction is hard, and 3- he may have had an underlying medical condition or just metabolized things differently than others to get cirrhosis so young. I'm having a difficult time with this and I can't talk to my family about it because they really think I'm crazy for being so sad. Maybe my cancer history has something to do with it.. I don't know.