and from the people I know who have divorced, I have a perfect strike rate
This is an interesting observation. I am curious on how many couples you know, and what is the ratio of them sleeping with 2 blankets. If 15/20 couples you know use 2 blankets, and 4 of them have divorced, then your theory has a high chance of coming true.
But I can see your point though. Being slightly inconvenienced is something expected in a relationship. It would support your theory more if they were initially using 1 blanket early on in their relationship, and then switched to two, leading up to the divorce.