She was isekai'd so she's mentally older even if she's naive.
Also, it seems like the plot is set back in the times when 30 year olds and such would marry 12 and 13 year old wives right out of debut. In all honesty it's not that bad if you choose to read the story in the time it was meant to...
He's trash and selfish. I hate that this actually happens in real life. So selfish for not letting her go even though he doesn't want to help keep the relationship going. I wish she was more confident and would find happiness herself.