A few months ago, my girlfriend broke up with me after we had an argument. (It was an online relationship and I know it sounds crazy, but we just clicked.) We were talking and she told me she had to think, so I let her go for a while. About 30 minutes later she finally called and we talked. I tried to come to a happy medium so we could both be content, but she told me no. And that she’s so sorry through her crying, she just ended it. Her reasoning was that she didn’t have time for me with school and money problems arising. I had always felt like there was more to it.
Flash forward to now (months later), she tells me her “best friend” at the time told her to break up with me. But he then went on to tell her that he had liked her a month after she broke up with me. She denied him, but it just upsets me. I feel like she shouldn’t have brought him into it at all on that level. Am I right to feel this way?
LemonVibe 
Honestly it doesn’t matter now, because your relationship is over. Let bygones be bygones and move on from her. She was already wanting to leave when she asked. Going over old drama won’t help you in any way.
I would also tell her that you would rather she didn’t give you this information since your relationship is over already and it only drags out drama or that you need some time to yourself before you can be friends again, which you do, because otherwise you wouldn’t have been in pain and needed to question old drama.
Going forward into your next relationship you may want to (super kindly in a non-confrontational manner NOT during a fight) tell your newest lady love that you would prefer that she comes to you first to talk about issues and communicate than to her friends. If she’s a rational person, she will agree, however you can’t forbid her from discussing relationship issues with her friends and if they are really friends they will want to be yours long term as well so they will give her good advice to help her and you meet in the middle.
I hope this helps and doesn’t sound judgmental towards you. I wish you the best of luck.
Yeah, what happened is kind of shitty, but the underlying issue isn’t that her friend tried to break you up. It’s that you had an online relationship, and you were trying to compete with a real-life friendship, platonic or otherwise.
My suggestion is to focus on pursuing real-life relationships yourself.