If you think about it, she just randomly "fell in love", sure they spent 1 year together, struggled due to the same person. She was afraid and he was someone by her side, but all I could see was a good build up for friendship at least for her. Since to her he was a 9 year old boy who needed someone by his side- While for the ML it makes sense, he was in love with her to begin with, the one who treated him well in moments of struggle as well as how much he yearns for her.
This leads to another thought of why she wants to keep holding on to this feeling.. "let me keep loving him" like HUH? I suppose that's alright- but 13 years???? Don't you think it's about time she moved on. And lastly, girl blushes whenever she receieves affection from Orsen, yet doesn't mean to even consider him? After around 10 years of knowing each other???
And lastly, the ML has no excuse, sure he missed her so much but it isn't an excuse to play another person's feelings.
The latest chapter (ch 62) clearly shows how the ML tried to reach out to her, and the letters were stopped somehow. Sure, you can say he put some effort? But in that time I think it says a lot on how disappointing their romance is going.
To begin with, the FL is mentally an adult, who fell for a possibly mentally adult 9 year old- And it's just a theory since he himself said things came naturally to him like he experienced it before? But it's never clarified. I don't really understand where her love comes from