Should I accept that I will be lonely for the rest of my life?

Nope. Things change quickly and over time. At 18, you have no clue what your life will turn out to be or how you will look or what is in store. You will be fine. Keep your head up, don't be so paranoid. Focus on things you can control like academics or your job. Become successful in small things, build on those and you will be more successful in big things. You are being way way too hard on yourself. You are so young! You will find happiness one day. Just keep your head up and make small goals to meet every day. Good luck!