I learned that there is a major difference between worrying and caring about someone:
Worrying is a concern about something that might happen in the future, something that isn't happening right now. If, for example, someone has a problem and you're worried about them, it means you are concerned that the problem might get worse or will lead to worse problems in the future (ex: that this person will develop an addiction, become depressed, commit suicide, etc.)
Caring, on the other hand, means that you care right now. You can care about the future also (most people who care would be worried about a problem getting worse, if that seems like a possibility), but you also care about what's going on with your friends in the given moment, regardless of the future. Like, if you knew for a fact that your friend would not suffer any long-term damage from something that's really hurting them right now, that everything will be okay later on, you would still care about the fact that something is hurting your friend right now.
Most of the time, people who worry about someone also care about them, but it's good to be forewarned that there are those who don't. There are those who are only worried that you'll hurt yourself or someone else, but show no interest in your problems once they confirm that you're not a threat to yourself, to others, or to your school/company's reputation or liability. There are those who didn't consider bullying to be a serious problem until kids started killing themselves and psych research showed negative long-term effects. So if you ever think you're being assessed for the threat you may pose, run the other way. Stick with people who care about what you're going through now, regardless of what it may lead to.