Style changes are always a wonderful gag.
Oh, so Marika's crush is actually obvious to others......
Which further proves how stupid this dude really is
Oh, he's not dumb at all. He thought they got along and they've been friends for a long time. He likes her and he thought that she kinda liked him back, but didn't know. Then he got the meter and became super confused because of what it looks like. Without the meter, he'd be aware of how she feels; often times his confusion is because she
seems to be happy and having a good time, but the meter looks... fucked up and weird, so now he doesn't know. The joke is that the love meter can't handle her feelings, so it's confusing to him, not that he's dense and doesn't get it.