I am so sorry for the loss of your beautiful sister 💐
I feel for you. We lost our sister coming up to four years this summer. She left behind children and her husband. He is a great dad and is very present for the two younger ones.
The eldest child lives with his fiancé.
My brother in law is single, he never goes anywhere without the kids, he works and his sister minds them. He talks about my sister all the time and was totally devoted to her during her sickness.
At this point I feel I could accept it if he met someone nice. It would be some company for him and someone he could laugh again with. My sister wouldn't have wanted him to be alone his whole life, he's only 40.
But I can understand your pain and despair at this short space of time.
On the other hand, my brother lost his wife after an illness, they didn't have a good marriage, they had split and for back together numerous times, there was no other people involved, it was just a volatile relationship.
Within a year he had met and married a lovely woman. Nothing like his wife, this one is so gentle, she holds down a job, she doesn't drink alcohol (the first wife had issues with alcohol) and they're so good together. There are no children involved in this instance and I think that makes a difference.
The relationship your bil is in may run its course.
I know my sister in law did tell my brother to move on, as did her family.