[SPOILERS AHEAD] imo it's not that weird (my opinion changed after getting more insight). He originally saved her because she had the same hair as his sister (tbh that's like their only similarity) and he feels guilty for his sister's death (suicide). He doesn't have any romantic feelings for her at that point and he's only helping her due to his own guilt. He thinks that if only he had believed in his sister and backed her up, she wouldn't have killed herself (an the man she loved would still be alive). Adrianna basically becomes a way for him to feel better abt her death. However after hanging out with her, he sees how she is absolutely nothing like his sister. They are like opposite ends of the spectrum. At this current moment in time, he does have feelings for her but he's in denial and he's using his sister as a shield.
it would be kinda weird if she ended up with him cuz of how similar she looks to his little sister and how much she reminds him of her like dude u wanna bang a copy of ur sister ??? if its like a mistranslation like how ppl call older gut friends oppa or whatever then its whatever