You are convicting the entire population for the "crimes" of one 14-year-old.
Secondly, if Julia doesn't date Mark, she is going to date someone, eventually. You will either handle it well and be supportive, or you will handle it poorly and lose her entirely.
Sooner or later you are going to date someone. Julia will either handle it well and still be your friend, or handle it poorly and pull a "my best friend's wedding" thing on you.
I am estimating your age at around 19 or 20. The next 3 years will represent huge changes for you. Be patient, thoughtful, and value the things you already have rather than minimizing them by wishing for more. Always be mindful and giving to those who have less than what you have - friends, a college degree, a limitless future. Cheers!