(((hugs))) You certainly are carrying a lot of stressful issues. You brother just might be angry at everything and nothing in particular (except those ppl or things that find his focus.) He's in a safe place for the time being, and it appears it's just what everyone needs.
I think you and your mom are doing the right thing. From here, she needs to speak with the doctors who are treating him and see how she should go about managing the meds better for him? They should be the ones to tell you the next step, and the one after, for your brother.
I'm sorry that you feel such a burden to be your brother's keeper. I think your desire to see a therapist is a good one. I don't know where you live (or even what country) but surely there are clinics or opportunities to see someone to talk to nearby?
Not everyone is put on meds because they are having difficulty dealing with difficult situations. Plus, you have the right to decide not to try meds anyway. Talk therapy is quite effective in helping most ppl with stressors.
I think first you do need to do some self care. Try and not take on the guilt of not being what you think your brother expects. I know you know that screaming at him to grow up isn't really a solution. People with mental health issues wouldn't be that way if it was under their control. Just like you are now feeling the stress of this situation, you are doing your best, right? Maybe your brother is doing his best too, with whatever malady he has?
There are thousands of ppl who can't pay their student loans right now. I doubt this is a permanent situation. How much contact have you have with those who collect the monies? Avoiding them will only add to your stress, I think.
You don't have to run away, but you do need some relief, imo. It's okay for you to go out for a day and just be yourself, and not be worrying about or taking care of things about your brother. Do you have any hobbies or activities you enjoy? Can you go to a movie? The library?
Can you see a counselor at the college you went to? Even if you don't go there anymore (I don't know if you do) you should be able to contact them. They have great resources for students and such that have so much on their plate.
Do good self care. Once you're feeling in control of your own world, you will then be able to decide what kind of a sister you can be for him, ok?
TC