I'm going to cause trouble for my best friend and one of his close freinds.
Why do you want to cause trouble between them?
Because I'm jealous that my friend spends so much of his time with his other friend.
I know you feel jealous of your friend and the relationship with another person, but it's wrong to have so much jealously of their relationship. You have to understand that your friends have other people in their life they want to spend time with. You need to give them some space and appreciate the time you do spend together.
Okay, but what should I do?
Perhaps try spending time with both of them. Or find out the things they do together and see if you're interested.