Is it possible that she could've seduced him without resorting to the Ant Nectar (I am guessing that's what the Nectar is)? Because to be frank, I'm sure all it would've taken was a day or two of being openly flirty with him and or just a good bit of booze along with some flirts, and they'd become a couple easily.
My two reasons are; one, due to him not being popular with girls in his previous life, he might fall for the pretty girls that are after him quickly; and two, As he has said before she would be just his type. He already thought she asked him out before so she could get to know him some and then get together with him.