Forgotten Title Not remember the novel name

Hiya. Im actually looking for a novel. I forgot the name but i remember the plot. The MC is the is the cousin of the heroine, and altought she had a boyfriend, the MC boyfriend also in love with her. MC marries her BF and they expecting a baby (husband dont know) , but the hubby not really care about her, just the heroine and our MC (and her unborn children) got killed because he not goes to save them.
MC got reborn some years before this and want to change everything.


i appreciate every help :3

 

I think it is " I Refuse to be a Supporting Character"

 

That it. Thank you so much ^^