in the last panel the guy doesn't say "you better not let me get bored" he actually says "I absolutely won't let you get bored". i.e. he thought a lot about ways to not let her get bored.
japanese can be a bit confusing due to implied pronouns.
the profile page here on mangadex kindly links to the raw, and this is the link to this particular chapter: https://www.pixiv.net/en/artworks/78484830
that bubble in particular says:
俺めちゃくちゃ色々考えたからな!
退屈なんてさせない! [ore mechakucha iroiro kangaeta kara na!
taikutsu nante sasenai!]
if you put it through MTL it'll say "Don't let me get bored!" but MTL sucks ass. literally is says "boredom such a thing won't allow". there is no "I" or "you" or "me" in that sentence, but the sentence before makes the meaning very clear. this is why I said that implied pronouns are tricky.