Reading this thread, it feels like you getting a girlfriend is what will prove your worth. I don't think it's as much about you actually having a girlfriend more than it is not wanting to feel like you're a total failure to your parents, those you feel don't want you to be happy, etc.
Because of my dysfunctional family, I grew up co-dependent without knowing it and didn't really have any boundaries. I was trampled all over while I gave everything to help anyone I could. If they were happy, I had value. If they were sad or upset, I wasn't doing enough and was worthless. I don't have that problem anymore.
My concern for you is that when you do get a date or a girlfriend (and I believe you will), you will have expectations that she cannot reach. You've already put her on a pedestal and the only way from there is down. When we have unhealthy attachments, hardly anything can truly be good because we aren't seeing clearly.
I used to compare myself to my siblings too. I have three siblings, one is married, one is in a good relationship finally away from her abusive past one and plans to be married and one who has sworn off relationships without having one. I, myself, am 36 with a 13 year old son. His dad (my first and only relationship) left us 6 years ago after being married for almost 7 years and he has been with another woman and I found out last year they have a son together. There's so much I didn't know about relationships that I know now and wish I did then.
Some here have already said these things, but there are questions we can ask ourselves. How much time, effort, money, etc. am I willing to give towards a romantic interest? If you don't like your schedule being interrupted, do you think you could make changes or tweak it any to involve your romantic interest? Can you set boundaries with your mother? If you can't set boundaries with her, you are likely to be taken advantage of by a future girlfriend and you don't need that at all. A book that helped me realize I even needed boundaries is Boundaries by Henry Cloud and John Townsend. It is Christian, but I believe it can be helpful to anyone because it helps you see where others end and you begin.
I know what it's like to be so depressed that nothing has color and there's an excuse for everything and how frustrating it is when people point it out because it truly feels like there's no way at all. But it seems like you have many supporters here and if you tried to focus on them and not on the the ones you feel hate you, I'm sure you can have a more positive, realistic outlook on your life and prospects. As a probably poor example, it's like those youtubers who make whole videos about their haters and barely recognize at all the ones who have supported them to become big channels. Why do the haters deserve any of your attention? So many people have poured into you so much wisdom, care, support and time here. It's hard to accept, but the only one stopping you from progressing is you.
@tree actually helped me a bit with this a long time ago. I was telling myself a very negative story and she pointed it out and I was frustrated and angry, because I didn't feel that I was. But, when I thought about her advice for a bit, I realized that I was telling a negative story and I told it to myself enough that I believed it, but it wasn't true.
What if you told yourself a good story? What if, instead of saying it's practically impossible and you have no chances that you instead say, "Hey, people have said good things about me. I do have some good characteristics. I can set boundaries with my mother no matter how difficult that may be. No matter how difficult and frustrating this is, I can keep trying and putting in effort to find a date that eventually will lead to a girlfriend and one day a wife. My siblings may already have relationships, but I'm not them, I'm me. I don't have to be like them or live up to them because there's no one like me in this world. I'm uniquely myself so I can't compare myself to anyone else. This is hard, but I can do it." And Markness, you surely can. =)