I need help with my parents. Please offer your opinion!?

I am a boy in 11th grade. I have a job at a law firm, filing, so I am able to make a reasonable amount of spending money for movies, clothes, itunes, etc. every month. Recently, I went on a week-long vacation with my girlfriend and her mother to Mexico. It cost about $1800, which I know is a lot, but I had never been on a trip of that sort so I figured I'd go. My parents didn't want to pay, so I figured I would pay for it. Unfortunately, I didn't have enough money in my bank account, so my girlfriend's mom said she would pay for my vacation package with her own and my girlfriend's, and I could just pay her back. That was in mid march. I now have payed her back about 1000 dollars, so it hasnt taken very long. I will be able to earn the other 800 in at least 2 1/2 months. Now I don't like being in debt and I look forward to being out of it, but I suppose I do not see it as the worst thing thats ever happened to me. Apperently my parents were "very negative" about the idea originally, and they say they tried to make me not go, but it seems to me that they let me go relatively easily, and they couldnt have really really disagreed with it that much. Now, however, comes the problem. I am in grade 11, and now my grade is planning the grad trip for next year. All of my friends are going, and I know that it is tacky to use the "but all of my friends are doing it" logic, but I feel like if I don't go, I will feel very lonely and left out for the week and all the time spent planning for it and anticipating it, and I will be dreading it up until it happens, and probably wishing I went for the weeks afterwards. I know this might not sound like a huge issue, but the truth is, I have had some pretty severe social issues and issues with friends during my time in high school, and I dread having to go through one again, especially sort of as my big end-of-high-school experience. I started off with two great male friends who I really loved spending time with, but they then both kinda decided they didnt like me anymore, and I was left alone. that is around the time I started to really get to know my girlfriend, and we just sort of bonded initially as friends because I was so lonely and sad about how things had gone, and I was overjoyed to have someone to talk to. I still feel grateful to her for that, though our relationship is about much more these days. Anyways, I spend most of grade 10 with just her as my one friend. I tried to talk to others, but I was so crushingly shy and, quite frankly, scared that I would just end up deserted again, that I had trouble making connections with many people. This year, fortunately, things have gone a bit better. I have started to make better friendships with people who were initially just my girlfriend's friends, and I, though still very shy, am a bit more comfortable in my own skin. I still get very lonely and depressed when I feel left out though, and I guess I simply dread going through times like that, which seem all too frequent to me. Ive often asked my parents about seeking therapy because I feel so bad so often, but they basically say that they never had therapy and teenagers are always angsty and I shjould "man up".Back to the Grad Trip... so basically I immediately returned home from Mexico and started hearing talk about the grad trip. I heard that the tour company were doing it with requires people to sign up like a year ahead, so my time was already running low. I brought it up with my parents, and they simply stated that I had just come back from a trip (though I payed for it myself) and they didnt want to pay for it, so i guess there was no way for me to go. I talked to my girlfriend about it, and she urged me to find a way, and even offered to front me the money. I agreed. She did it because she knows how upset I get and she is the one always having to deal with my being upset about my isolation and my two-week-long pannic attacks/depressions (which is basically what they are), so she thought, though I am in debt, and debt is bad, its simply not worth going through what i would go through to miss something that is such a big deal. I agreed, and lent her the money. Now my parents are furious, saying they may not even let me go at all, I should never have been lended the money for Mexico from my girlfriends mom, a middle aged woman, because that is "creepy" they refuse to pay for it, and they would rather i not be in debt than I be not be incredibly upset/left out and lonely. I understand that I do need to learn financial lessons, and i need to learn to not get myself into debt, but i simply feel that I cant put myself through the stress of being left out and lonely again, and Ive always been a well-behaved, hard working son, I dont ask them to pay for much, and many students' parents are paying for their children's trips, so i dont see why my parents cant. i just want to know if you think I am j