He isn't stupid. It's just that his mind works so fast that he can't concentrate sometimes. He wishes they would get that. They are his team, his friends (his family). He wanted to scream when they split up. They are his family, dang it! Don't they get that?! It's not like most people like him (even if mostly they just tolerate him), you know. He'll never tell them how much they mean to him. He'll never tell them how much it matters to have them pay attention to him (mostly), like him (kinda), listen to him (sometimes). He's not stupid. He's just really good at denial. So good, that he has convinced himself that they care about him. So it doesn't matter that batman keeps on brushing him off. Batman's always grumpy (but not to superman, and he's worst to him out of all the members). So what if hawk girl and wonder woman brush him off whenever he flirts. They're not interested in him and he's not interested in them (he just wants them to pay attention to him). And yeah, superman is pretty overprotective of him but he's over protective of everyone(he doesn't treat them like idiots though, doesn't tell them to stay out of trouble). And okay, john still hasn't realized he likes him, so what. John's straight and has a girlfriend (those 'are you stupid' looks usually come up most when he's trying to impress him).
He's not stupid. He's just really good at denial.