@pinetsun
That does sound pretty horrible. Having someone betray your trust is never a good feeling. Just don't forget that there
are good, trustworthy people out there. It's good for you to realize that your friend 'A' was actually an awful friend, as you definitely shouldn't tolerate actions like those, and you should seek out better friends.
If this person keeps harassing you, don't give them an inch, i.e. don't let them know how it negatively affects you. Judging by their presumed immaturity, they could possibly see you as more of a target and assume that you won't fight back. Just go about your business and strive to do whatever it is you want to do. Most often, when a harasser sees that their target isn't affected by their provocations, they will become bored and stop what they're doing. It may take time, but my advice is try not to let Friend A's actions dictate your
own actions and feelings too much. You're your own person, and
you know who you really are, so there's also no reason to allow someone else's petty criticism to get you down.
Best of luck, friendo.