Ok, so you need a change of environment where you learn meaningful skills, with your mind and body. Fine. But this can take many forms. The classical solution for 20-somethings is to go “travel the world and find yourself” ..whatever that means. I do not think that solution sounds very attractive to you, and I am sure that you would have a hard time selling it to your social environment. What you need is an activity, a learning environment, with a clear agenda. You need to go somewhere new where you have a clear role, use your body, will be able to get into a flow and learn useful skills. And it should give you something real like a certificate and skills that you can use when you are back in your own environment. Yes, I know it sounds childish to want a paper, and of course it is not about the diploma or paper itself, but it is about a clear mark of achievement that you and your social environment can accept and understand. That will make it much easier to get on that plane with a good feeling and the blessings of your family and friends.
Your significant others might not like this idea of going away by yourself for a few months. But think about it this way: what is the alternative? Surely, nobody who loves you wants to watch you disappear a little more behind the same, sad, tired face. (If they are actually ok with that, well…). Sooner or later, something needs to be done, something needs to change, like it or not. If you do not do it, something will, and you are probably not going to like it, and neither are they.
Tell them the truth:"I am not okay, and I found something that has actually worked for people like me." Explain it. Let them read this text. Assure them that you are not going away to be a beach bum acting out a classical cliché midlife-crisis. You are going to do a challenging program and will come back healthier and with a certificate to prove you are a Divemaster.