Yes there is a way to say no without being a jackass. Just say "No." I'm just being cute. But it's true too. Just because you say "no" doesn't mean you're a jackass. It might mean the person you're saying no to will feel upset though. And while you are not in existence to calm his feelings, sure, it would be a good thing to be kind about it. You could say "I really need my space right now." You could also ask him why he stays over so much, like why is he afraid to be alone? If you want to know. It might help you understand. But you can always say no. Maybe he's struggling with something. You won't know unless you ask. If you think it might make him upset or hurt his feelings, you could try to soften it by saying you value his friendship, but that you need to limit the amt. of time people are spending overnight at your house.