Oh boy Seo, I think second guessing ourselves is a large part of this process of detachment, all those thoughts you are having are exactly the kinds of thoughts I have and I believe most of us have. You can't help it, there is no road map for this, you are in fact going against your own instincts to nurture, protect, care for, love, provide for..........And, you want so much for him to change and heal and for it to work, that you LOOK for anything that will prove that he is.
You have to change the dynamic of enabling which means you have to now define what that is, see when you are doing it and stop it. You have to learn to differentiate enabling from loving kindness because the lines between those have been severely blurred for you. You must take a step back and allow someone you love dearly to suffer the natural consequences of his behavior, while staying on the sidelines doing nothing............when the likelihood is if you stepped in you could make it easier for him, you could save him. You have to learn to live with the remarkable discomfort and anxiety of stopping your behavior, your enabling, which is why many of us continue stepping in to help, we can't live with that anxiety. That is a huge part of this, being able to feel all that anxiety and let our kids face their own consequences.
Only you can decide what is enough and when you've reached the point where you need to allow him to experience the consequences of his behavior without your assistance. It is easier to detach when we are angry, once we are not, and we see some humanity in them, some kindness, we begin second guessing ourselves.
Seo, as you can see, this is a treacherous experience for us. You mentioned you had support from your friends, your husband and your family, which is a huge asset. I would still encourage you to seek out a professional, a therapist who is trained in this so he/she could guide you through these feelings and offer you not only support, but clearly defined boundaries for you to set, tools to understand how this all works and understanding of what your role now has to be in order for you to detach and learn to accept what is. That acceptance is very, very hard for us because for the most part, we continue to feel as if WE can do something, anything to impact the end result. The truth is we can't. We are essentially powerless to enact change in another, only they can do that.
Your regret, your guilt, your love for him, your hope, your second guessing yourself are all parts of this process which keep us stuck in the same behaviors. It becomes about changing those feelings within ourselves, understanding the difference between love and enabling, realizing that our kids make choices and they must be responsible for their actions and deal with the consequences, even when those consequences are so hard for US to allow. If you are working harder then he is, then you need to stop. If you are feeling resentments, then you need to look at what you are doing.
He was nice while you were doing all the work for him, of course he was, once you give that role back to him, you may see his "niceness" turn to real anger, that's usually what happens, as soon as they can't get us to do it for them, we are blamed and all the anger gets turned on us. Didn't you say he threatened you when he was younger because you set a punishment? I doubt that will change now. They are master manipulators and know how to push our buttons.
Once you learn how to set boundaries, then you must keep those boundaries intact. If you give in, then it is for naught, your word ceases to matter, no one will believe you anymore. You set boundaries and then you hold them, you hold that line, he cannot cross it, you keep your word, you force him to figure it out, make other choices. Otherwise, what's the point of setting the boundary if you yourself don't uphold it?
We are only human, having to step back and distance ourselves from our adult children is a horror, it is something none of us know how to do and all of us make mistakes and all of us suffer greatly. That is why I always, always recommend that parents get help, therapy is an excellent tool, but parent groups, NAMI groups, 12 step groups, any kind of group will help. Your friends and family, although they can put their arms around you and comfort you, don't usually know any more then you do about how to do this, so often professional support is necessary, it just makes it easier. Doing it alone is treacherous and all the self doubts can catapult us right back to where we were and keep us stuck in the same cycles. Seo, this is hard, perhaps the hardest thing you are ever going to do, all your feelings are normal and valid, I hope you find someone to guide you through it.