Isn't this immature and lame?

Some of my friends are mad at me because I'm buddies with a gal they don't like. Yasee, I got invited to this girl's bachelorette party & now one of my friends won't speak to me cause she's mad I went. (She hates the girl getting married) My cousin, (who also hates the soon-to-be bride) makes snide comments that I went & is always insulting. I swear, no 2 of my friends get along! What's the best way to deal with this? My GOD they're nearly 30 years old!