Notice in the last page, the Succubus was reading some kind of magazine of erotic men or something, but inside of it she's actually reading pure love books she has in one of earlier chapters (from the sentence in the book that says, "That day, two people (something, I can't read it), they did a pure kiss!".
That note. He's trying. Like this guy below said, if there's an ending to this manga strips (when they finally have sex), it'd be amazing thanks to it. Dude is actually clever (like how he remembers those mushrooms in earlier chapter) and analytical.