I think it was in the first chapter but i believe the first time Rui tried anything with Shion he didnt realize it was Shion to begin with until he saw the scar.
Probably cus shion was a major fuckboi, like who hits on a straight fuckboi. We did see that rui liked inviting shion over to have sex with him tho
Because of your question, I reread this manga again.. haha.. and yup, Rui definitely like Shion way before~ it’s just that, he is scared to be rejected by Shion so he chose to be his best friend only.. plus Shion always like women so yeah..
He stated that he was scared to ruin their friendship when shion was a man and at the first chapter he didn't know it was shipn utill he saw the scar(plus he said that he was happy just being by his side)
I know he said he fell in love with him as a man, but the fact that he didnt actually try anything until he became a woman is so confusing to me. Why put him through all that?