It's not an obligation, it's an offer.

[Seriously, he's being so nonchalant about offering up his bed. If only because it seriously caused zero hardship for him last night and so he finds it hard to mind.]

If you sleep better with me, then it's kind of a compliment. [But teasing aside-] If it helps you rest better and you don't mind me taking up space, then it's not like it's a problem for me, Aria-chan.