I haven't read any advance translated chapters for this (as im only reading in Mangago)
but to your question: I think Rum eventually realised that Ginger likes him. as for Ginger choosing to be a demon - It was also only Ginger's assumption that Rum will not like him as an angel. Ginger NEVER asked Rum what his real thoughts are. he was too self-absorbed with his own pain and fear of rejection that he never truly looked at Rum nor did he listen.
Spoilers down below
As to answer your question from the Korean raws I've read for the extra chapters, Rum has noticed Ginger liking him a long time ago, and has been waiting for Ginger to confess so that he can answer back to his feelings. ヾ(❀╹◡╹)ﾉ~
Pls i just come to the conclusionnnn plss answer me butt this maybe include a SPOILER for those who doesnt read this manga yet
GUYS
DID RUM INTENTIONALLY act that he dont know about gin feeling for him but truthfully he knows because he want gin to become an angel causee being an angel is better for him orr is good for gin or rum has another reason
Cause of that maybe rum afraid or doesnt want gin to choose being demon because of him
What do you guys think??
Well this is just come in my mind
I dont really understand english so i justt look at the comment section andd yeahh hehe(●￣(ｴ)￣●)