I'm not going to see or talk to my friend who was having a bad day
Why are you avoiding your friend like that?
I don't want to get involved in boring stuff.
Your friends troubles shouldn't be boring to you. That's not being a supportive friend. You should reach out to them if they're having a bad  day, even if it doesn't feel exciting to you.
I'm going to lose them one day.
You will lose friendships if you're not supportive. Maybe you can reach out to them and suggest something fun to do that might help cheer them up? That way you'll both be engaged in something exciting to your mutual benefit.