It's OK to cry at an Al-Anon or Alateen meeting. Lots of people do at one time or another--it isn't like you'll be the first one to cry! I've heard a lot of people cry through lots of meetings, especially in the beginning or when something really bad happens or when they are just totally stressed out.
Nobody will think badly of you--they understand because they are dealing with the same things with their parents, brother or sister, grandparents, aunts/uncles, best friends, boyfriends and girlfriends. Being around alcoholic drinking is very stressful to families and friends. Please at least try a meeting or two. I think you would find it really helpful.
I hope you will keep posting here a whole bunch, too!
Hugs,