Welcome here, this is a place where you will be listened to, valued and may even get some encouragement and suggestions that might help. Deciding to post here was a good move.
I'm sure there are many good moves inside you. Reading I get the impress on of someone who is sensitive, has insight into herself around her, and is caring. Someone to value.
If a person is constantly put down, by word or action, or not valued then they start to lose self-worth. I don't know why.
Your life has been very hard -so far. A father often absent, and wiht a silly idea of what you ought to be. A mother preoccupied with your brother and failing as a result to see the efforts and successes you have made.
A brother who is someone you worry about, plus being bullied.
It is no wonder you feel like you do, and as you have worked out trying to get into relations with users is no answer -quite the opposite. Perhaps I'm misunderstanding or reading too much into what you say, but trying to do anything to please those abusive people so you would be accepted and liked is never going to work out well, you just end up feeling isolated and worse.
Look, I'm not saying anything you do not already know. The important thing is for you - not others - to feel your strength, intelligence, abilities empathy and worth. Not something that happens overnight but you can get there.
It may take help, All the thoughts you describe: the not good enoughs, the being lost, unmotivated and all the rest sound like me when I've had a bout of depression which I get with my anxiety. I never improved or got out of this trap on my own.
May I suggest you see your GP in a long consultation and say how you feel, be tested for anxiety and depression and then see what happens. You may be offered therapy -or meds - or both. It can be the start, it was for me.
If you feel that face to face explanations might be just too hard then spend a day or so writing everything down (point form is good) and share the paper in the consultation. That makes it a lot easier.
With relationships there are good people out there who will value you properly - for your character and nature. They may be hard to recognize at first as those you are used to -or people like them - are easy for you to join up with (it's familiar territory), but worth the effort, not only for you , but for them too, as they end up with someone who has understanding and all the fine qualities I listed before.
Please talk some more