I need some advice.
You are not over reacting at all. You even tried to give it a go when it wasn’t your ideal situation. How rude can these people be to then tell you that you’re the bad one for wanting out, sounds manipulative to me.
Relationships are a 2 way street, if all you’re getting from it is a headache it surely can’t be worth staying for. As you say - you’re in a relationship with the son not the father. You don’t owe the father anything, he should be thanking you for being supportive and yet he’s degrading you?
It’s really thoughtful of you asking to leave but for your own sanity I don’t think you should be seeking permission to leave. You can still be in a relationship without living together. You can still be in a relationship without shared finances. If you need to find someone to replace you for the lease do it. I wouldn’t want to stay trapped in that situation for another second if I were you. If a relationship is taking more from you than giving you it’s not worth it. If your partner isn’t ok with you moving out that’s his problem and his decision if he wants to keep a relationship with you or with his dad, or figure out his own method to keep both of you happy. That decision shouldn’t be one on your shoulders.
You’ve stated your needs, your partner needs to respect them. You don’t have to be part of the fathers life if it’s not good for you. Family should not be allowed unconditional love at the expense of your happiness.