You're not in a situation to get a job, and that's okay. Your money issues aren't that terrible that there isn't a solution.
The boyfriend - have you spoken to him about the issue? If you're having such trouble at home, he needs to step it up and take care of you for once. You can't be expected to maintain the relationship yourself, it seems pretty one-sided from what you've written here. He knows you're taking care of your brother and getting ready for college, he needs to step up his own effort to help you out. That's part of being in a relationship. If he's not willing to help you out when you need it, you might want to reconsider this relationship.
As for your school trip - have you spoken with your teacher? They can't make a trip a requirement if there is a possiblity that their students can't afford the trip. This is a solution best solved by talking to the teacher. You can email them if you don't have the time, or give them a call and set up a meeting. Let them know what's going on - the teacher/school might be able to help you fund the trip.
For college - it's not as bad as you think. I have my bachelors and am currently working on my masters (full time). Have you looked into scholarship possiblities? Some universities automatically give you scholarships based on your GPA (grade point average) and the extracurriculars you are involved with on campus. There are also "hidden" scholarships that you don't hear about during your first year - these are departmental scholarships, only offered to people within your department (your major). You can apply to dozens of scholarships to help cover tuition, and, check with your school about work-study. From the context of your paragraphs I'm going to guess you're European, so I don't know if work-study is available for you, but it couldn't hurt to ask.
Work-study is a part-time job in exchange for pay (usually minimum wage) and the government provides a portion of your tuition (for FREE). You work a max of 20 hours per week.
Outside of that, there are dozens of way to save cash while you're in school. Of course, cut down on name-brand stuff, but one BIG thing you can do is order your textbooks online! Amazon.com and Half.com are AWESOME places to buy books - as well as Facebook Martketplace, Craigslist.com, and even billboards around campus. You might also qualify for grants, depending on your family's income and whether or not you are a dependent.
There are also plenty of advisors and people on campus who can help you manage your finances (and find scholarships/grants/work that isn't widely known) to make things less scary.
It is surprisingly easy to manage paying back your student loans. For me, I don't know if it's the same for your country, there are dozens of options to pay - you can have payments based on your income (called "income-contingent"), you can pay the standard rate, a low rate, a higher rate, you can apply for forbearance on your loans should you be unable to pay for a certain amount of time or you choose to go back to school. The forbearance means you won't have to pay until an agreed upon date with your lender (interest will still accrue, but it's usually low depending on how you get the loan).
I have been able to pay back very well and I have a very low income (less than $25K).
....so, take a pause and breathe. It's not as terrifying as it seems (I've been through it once already!). Things may feel like they're piling on you, but when you're stressed out, things that don't normally bother you will feel like the weight of the world.
Here's something I encourage - take some "me" time. I know it seems damn near impossible, but if you schedule your time well, you can find at least half a day to relax. You need to have some relaxing time to keep yourself sane. There's no way around that. If you do a little extra work each day and get ahead, you can free up an afternoon to do things you enjoy. Or, if you don't want to work a little more to free up one day, just take 20 minutes a day and go for a walk in a scenic, private location. Grab your iPod if you have one. It sounds very cliche, and it is, but this saved me my first year of teaching.
You'll make it. Talk to your teacher hosting the class, talk to your boyfriend, and use the resources for your college to help find ways to finance your education. It's possible.