Never be too busy for the ones that love you. One day, they will take your excuse to heart and move on. There is never a reason to be "too busy" for a person who has 'been there' for you from the start of your friendship. Remember that before you treat them like an option
Hang out with people who don't just make you happy, but treat others well. They reflect off of your character. It is better to have less real "quality" friends than a ton of friends who treat others badly!