The blonde dude doesn't even like her like that. He wants to marry her to see if marriage is really his thing. I will run run away too if I find out that my husband to be doesn't like me. Also, the blond dude gets on my nerves. Like the Fl did all she could to get him know that she does not want to marry him anymore but he still won't leave her alone.
I mean it's worth noting how things change near the end. She realizes it was a cruel move, he learns to understand why she did it, and they come to a compromise. I don't think the author is trying to say that what she did was the right thing to do considering she changed her approach after talking to him with sincerity. She changed and she grew to be more thoughtful towards him and her family.

I don’t want to be that one woke friend but the fl is such an asshole for literally running off at her wedding…imagine if she was a guy and the groom was a girl, everyone would actually hate the fl (rightfully). There was so many better ways to do it and she did it horribly so I don’t really like her tbh