Why do some friends get upset when you have other friends (or a life) outside of them?

For example:

- If you mention other friends, they get visibly upset
- If you are hang out with other friends, they seem annoyed or ask a bunch of questions about these friends
- If life gets busy for you, they scold you for not spending enough time with them
Why do some friends get upset when you have other friends (or a life) outside of them?
Post Opinion