Why do people do this

One of the things that I don't understand is why people tend to keep associating with people whom they don't like or seriously loathe.

Meanwhile, they put out many red flags

1. They constantly criticize them
2. They compete with them
3. They make plans and bail with bizarre excuses
4. They constantly yell or snap at them
5. They constantly treat them like they are a pest by nagging at them
6. They jerk them around
7. They are not excited to see them
8. They don't seem too sad if plans don't work out
9. The other person can't be themselves around them
10. The other person often feels empty or sick after