I'm thinking of befriending the ex boyfriend's friends
Why do you want to be friends with your ex's friends so much?
Because I think they are a kind person
It's understandable to want to be friends with people, but making friends them might make things uncomfortable for everyone since they are friends with your ex. I think it would be best to instead find friends who aren't associated with your ex.
But I don't care about my ex. I hate him.
It's common to feel angry and frustrated at an ex after a breakup, but it's good to just move on. Dwelling on the past makes it difficult to find new and better relationships with other people. I think you should look for new people to spend time with instead of worrying about your ex.