Arthur is a succubus (technically an incubus because he's maleβ¦), and he puts of mating until he's almost fainting from hunger (succubi/incubi are sex demons that are usually depicted as needing sexual energy in order to survive). The reason he keeps doing this is because he believes that Al always refers to it as "feeding" him; plus he was unclear when he said "I really hate this" (he didn't voice the part that he actually hated - doing it while Arthur could barely move), so he thinks that Al is only with him out of a sense of duty.
On the other hand, because Arthur always puts off having sex, Al thinks he actually hates it ("it's as if we can only have sex because I force him to"), which is another part that he hates - but since he loves Arthur, he doesn't want him to die, so he makes sure to sustain him!
(β'β‘'β)οΎ ~ It's a story of mutual love combined with mutual misunderstandings! ~ (ββ½β)
What going on in this Manga ???