@scarlet_summer
It's already romantic, at least on his end. She asked if he saw her as a mother he said not exactly and specified that "her hand felt like a mother's hand and he wanted to keep holding it forever" while blushing. He said that was "back then," and then asked her to imagine what it would be like if they were high school students together, then imagined himself blushing because she looked at him.
This is only gonna end one of two ways: either they both like each other, but she can't accept it and they go their separate ways, or they get together. There is a 0% chance this will end with them as true platonic friends. There is too much underlying tension for that to be stable. He's clearly interested in her romantically and is only holding back because of her. She has some feelings she is repressing because it feels morally wrong. I don't think his feelings will waver from love and admiration, the only changes I foresee will be on her end.
If they do remain "just friends" it will be because of moral guilt, with both of them suppressing their feelings. Not saying this is for the best, but I'm quite confident this is how it will go just based on stuff I've read in the past. Authors like drama and big emotions.