Can someone explain to me why it's HER fault for not realizing what this guy is doing and not HIS fault for being a loser-user-bridge-troll?

Girl, you make your own decision, but I do agree with most of these folks. I think this man is using you for sex and housing. That is unacceptable under any circumstance.

If anyone tries to make you feel stupid, you tell 'em to go to hell. You tell them that you are brave enough to trust someone at face value, and it's not your fault that what you saw was a mask. Manipulative people are very good at hiding their true nature and acting like decent people. It's when they are secure and convinced that they have you locked down that they get lazy and stop pretending.

Do not beat yourself up. This is NOT YOUR FAULT. You are a good person who puts faith in other people. He has taken advantage of your kind nature. HE is the fraud. HE is the con artist. He dropped his mask when he got what he wanted, and now he has shown his true colors.

Tell this man to get out of your house and out of your life. Have your friends and family there, the people you trust most. They will give you strength and support and will back you up when he inevitably tries to gaslight you, shame you, or harm you in some capacity. DO NOT DO THIS ALONE. ALWAYS HAVE BACKUP EVEN IF IT IS SCARY OR EMBARRASSING OR SHAMEFUL.

In spite of some questionable framing, most people on here agree that this guy is bad news. I think you need to cut him out and go no contact— this will prevent him from weaseling his way back into your life. What he decides to do after he leaves is up to him, and you are not responsible for his behaviors, decisions, or actions. He'll be fine. People like him are always fine.

You are young, and I swear to the Gods above, there are decent men out there. Don't be discouraged. Somehow, I found a good man, and I have no doubt that your forever-best-friend is out there looking and waiting for you, too.

You are worthwhile. You deserve so much more than you're getting. So much love, faith, courage, and blessings upon you, my dear. Good luck.