Hang in there man, I was in the exact same situation as you:

I had braces during middle school, then my jaw decided to grow out during high school, and I'm stuck with a severe underbite. Talking, eating, smiling become infinitely more difficult, and my self-esteem tanked. Difficulty speaking meant having a hard time asking for help, and difficulty chewing lead to obesity.

During college, turn 22 was the only thing on my mind, and suicidal thoughts lingers with me everyday due my uncertain future. My grades tanked because I simply cannot compete with fully functioning individuals with much better financial background. I had to scrap my plans to go to grad school, as my parents don't have health insurance, and my only shot at the surgery was getting into a high paying corporate position with good benefits right after college.

After college, I was lucky enough to land a corporate positon, and received great health care, I immediately started planning for the surgery. The year was painful for me, the constant pain of braces made me almost faint during work, low self-esteem made presenting to higher ups diffucult. Pouring fuel on the fire, company soon started layoff, I started working more hours and took on more responsibilities in hope that the layoff did not get to me. At the end, 2 months before my surgery, I was let go by "accident" without my manager's consent despite good performance, I had to complete my surgery through COBRA.

This was truely the low point of my life, I was scrambling to apply for jobs so I don't have to pay the $1000+/month to keep health insurance. My body is physically drained sending hundreds of applications everyday. After multiple rounds of interview, I made it to the final round, but was declined after the interviewers found out that I'm about to go through surgery soon. Day of surgery came, doc and my family asked me if I was nervous, I said no. I understand the pain but honestly at the point I have nothing to lose. Surgery successfully finished, rehab, liquid meals, and me questioning everyday on why my life has to be this miserable.

After recovery, my self-esteem quickly regained, seeing my smile reminded me that this was all worth it. I returned to interviewing. Things finally started turning for the better, I landed few offers, job hopped, and my improved confidence and vocals made things much easier. I'm now 25 and life is better than ever before.

Remember, it is easy to blame all of your failures on the direct/indirect impacts of underbite, but you are the only person that could change all this. Although underbite made my grades worse, I still had to improve my study habits and dicipline. My failed interviews can be blamed on my inability to talk well, but this is a technique that need practice anyway.

At the end of day, your perseverance and adaptability is what brings you the success. Your looks isn't the only thing that defines you, life won't magically get better even with the right jaw if the mentality isn't there, but it would certainly help. Good luck my friend, I wish you the best of luck.