Well dear one, you established a boundary. He obviously had no respect for it or may have sincerely forgot. Or, and this is my guess, like a rebellious child, he was testing you to see if you would cave. You did. He now feels like he can do what he wants. They all think that they can handle it on their own until they stop being enabled and hit rock bottom.
This is going to sound harsh, but so what if he has no where to go? Would i throw a sick person out? No, not generally. But let's say he has Ebola. Do you kick him out because you're mean or do you kick him out to stop him from infecting the rest of the village? He is infectious and making you ill. It most certainly is your problem too if everything is left to you. Even his parents know that and they don't want the infection in their home.
Protect yourself. Make a plan for your financial and legal safety. After you've made your plan, stick to it. It will be hard because you are not cruel, thoughtless and self centered. But it's only going to get worse if you don't(((Hugs))))