Why do friends get jealous of your boyfriend and they dont even know them?

there are at least a few of reasons i can think of.

1. they might feel a sense of inadequacy next to you. you have something of a quality that they want but do not feel they can get

2. if you are now spending more time with the boy and less with them, again there may be a sense of inadequacy that you would rather spend time with this other person over them.

3. they dont and you are misperceiving the situation