mimi0108
@Kokuto I see what you mean and, indeed, it is possible that he didn't assume his feelings before having the poison love bug x)
For me, I see it like this: he's been aware of having feelings for her since episode 7, as shown by the times he tries to pat her on the head, the looks he gives her and so on. But the poison love bug is a test for him. He's never known romantic love but he feels that must be how he feels about XY. He is physically attracted to her and thinks to have feelings for her. He also feels like she must have feelings for him since she made the poisonous bug for him (even though she didn't know what she was doing, the bug couple was raised because she was thinking of XL and therefore a part of her loved him enough for the bugs to smell it and flourish). He thinks XY is alone like him and unattached. She is "doomed" anyway since she has the bug in her. Therefore, he wants to have the bug both out of curiosity (to see what romantic love is and if it's what he was feeling) but also to not be alone and have this connection with someone. He almost begs her to transfer the poisonous bug to him, which was comical.
But that's my opinion and, anyway, unless we have a scene telling us precisely when it was, we are all free to interpret as we feel and I love it because it's interesting to see how each interpret scenes x)
Okay, after forcing myself to re-watch some XL scenes -- for research only, RESEARCH, I say -- I have to say, I don't think the moment of falling in love was the moon light walking scene. Because it was Episode 8 where XY tried to infest XL with the Poison Love Bug and it refused to enter him -- ostensibly because there was not love between them. Of course, this doesn't mean XL has no feelings for XY before then. It just means, it isn't recognizably love?
There's several reasons for him to accept XY's request to take on the Poison Love Bug. He also plans on killing CX, and he knows that will kill XY also, which, no matter what his feelings, he doesn't want to happen.
I'd forgotten that she was raising the bug with him in mind. It's interesting that she can't create a poison that effects him, EXCEPT for love. And arguably, since she keeps standing in the way of him killing CX, that's what kills him.