Feeling like worth nothing

So lately I’ve been like I’m worth nothing. The only thing I had ever had going for me was school, I used to have excellent grades, but then, I got to college and wanted to get into medecine. But I don’t have the R-score (which compares your grades to other and takes in consideration how strong your class is) to go into medecine in Quebec. So I opted for nutrition, but even then, I don’t have the R-score for that. I decided to go into another province to study in nutrition but it’s so expensive and my dad doesn’t support me in this at all. He thinks that because I’ve failed so badly in college here that I’m gonna fail even more in another province and it’s gonna be expensive as fuck (20k a year) whereas here it wouldn’t (4k a year). But he doesn’t understand that the way our grades are graded here is different from other provinces which gives me a significant better chance at getting into nutrition in another province. I’ve explained this to him multiple times but he doesn’t even believe me wanting to go into nutrition because I always wanted to go into medecine but I just don’t have the fucking grades. I’ve told him that I’d be the one in debt and not him but he doesn’t care and he’s not supportive. In addition to this, I’m 18 and been single all my life, all of my friends are now in their second serious relationship and I have never been in one. I feel like utter bullshit because I’m always used for sex, friend zone or everyone’s second choice. Nobody gets it when I say this makes me sad but it really does. People having cheated on their S/O get boyfriends/girlfriends more easily than I do. I’m tired of feeling like I’m worth like shit and like I’m not worth anything. A literal fly deserves more oxygen than I do. There’s literally no point in continuing anything because it seems like I’m never going to do something I want in life (medecine, nutrition) and end up alone. I don’t know what to do. What am I doing wrong???