We feel a natural responsibility towards people. Especially when we have shared some part of our lives with them and have built bonds with them. It can be hard to leave people behind when you've seen the good side of them. But how far do you take it? An extreme example is cleaning your blood out of the carpet and making excuses for the guy who beat you. A less extreme, but parallel example is putting up with a torrent of needling, whining, devious, intelligently manipulative abuse from an ex because you know he is lonely and unhappy.
Life is a beautifully and hopelessly complex web of human relations and interactions. We all bounce around, affecting and influencing the people we meet for better or worse. Your outlook on life and your situation has been moulded by hundreds of different people over the past 24 years. Some you met for a moment, some you have known for decades. Some impacts have been minor and some have competely altered the course of your life.
We cannot claim and accept responsibility for everybody we meet. We are not able to juggle the needs and priorities of everone. We could not possibly be reasonably expected to do so. The best we can do is single out that small band of people who mean the most to us and try to be good to them. Each of us creates our own little tribe of people we love. Mum, Dad, Kai, Paul, Bevis, Callum...whoever means a lot to you - genuinely fucking matters to you - you should look out for, and expect the same in return from them.
You are NOT responsible for everyone. It's sweet that you want to be but it will end up hurting you. As you said earlier, you cant have an open door permanently for everybody to dump their worries on you. You have your own problems that need your attention and you're working on them and struggling with them. One of the methods by which you can improve your situation is cutting the negative things out of your life using a blunt knife.