I wished I could talk to him as we used to do but he doesn't come out of his room anymore. I've ruined it I think.
I think you're being much too hard on yourself. You keep saying you don't think you are open minded, pro-free love, etc., but I'm not getting that impression at all from what you're written here about the specific things that have happened.
You work, you pay for the house you and your sons live in (even if they are now contributing) and you need peace and quiet overnight. You're already being accommodating by trying earplugs and allowing more noise on weekends when you don't have to work the next day. But people who live together coming together to set reasonable compromise boundaries that work for everyone is NORMAL. Look how many hotels (just for example) enforce quiet hours from mid-evening to early morning. People need quiet to sleep. People with ongoing obligations, such as your job, need quiet and sleep at predictable and specific times.
I would let your son's girlfriend stay (if that's what they want and it's not causing other problems), but they like everyone else in the house MUST observe the quiet hours. As your other son is able to do this, it's possible. (And believe me - if your younger son were in a share house with housemates his own age, they would not be putting up with noise all night every night either! They might also not like essentially having an additional non-paying roommate, if she's staying more nights than she's going home.)
Your younger son is being quite immature if he's intentionally avoiding discussing this with you; it's possible there could be compromises such as his using a different room, but not if he's not interested in exploring them. Don't be bulldozed into doing more than you can do. You matter too, and have every right to have your needs listened to, respected, and accommodated (within reason).