Help me decide?

Guy B probably told guy A already if they're actually good friends and he's not a snake lol.

All of these guys are somewhat toxic and narcissistic
None genuinely like you and it's obvious you don't really like them either, because you can't even keep a friendship with them going because of their attitudes

Bin the three of them and broaden your horizons op

I don’t think you should tell him unless he asks what you’ve been up to. Guy A is just a FWB, at the end of the day, so only just wanting sex is his position with you. Guy B just used his opportunity to talk to you while you were single, which is Okay. The feelings were mutual too.

I do think you’re indecisive. You keep just jumping from guy to guy. Chances are that when you get with guy A, you will still go back to guy B and then back to guy C. Your history demonstrably shows you’re capable of doing that, I don’t really think you want the commitment.

I say you to tell him, chances are guy B is either going to tell him or already has so I think guy A will appreciate the honesty.

Guy A and I ended up being really good friends as we'd always talk during that one class when it was just us, not being judged by his other popular friends. We ended up being really close, a senior of mine tried forcefully hitting on me and stuff once, and Guy A was the first person I told, he was very supportive, unlike my bf at that time, and made me feel much better about that incident. Guy A got to be more vulnerable around me, he didnt have to seem like a perfect person like he'd have to be around his other friends. The FWB thing wasnt extreme either, we never had s*x, just kissing and stuff.
I've never wanted to go back to Guy B, he just suddenly became supportive and understanding and listened when I was in a really bad place with Guy C. Guy A used to be my rebound (he knows that too), but I think its how he's changed, thats got me confused about where we stand.

Yea they all used to be somewhat toxic/narcissistic, but Guy A's been acting real different lately. We moved on from the fwb infactuation, and now I like talking with him, even though sometimes he gets busy and we dont talk for days. When he does talk though, he's been more open and suggestive of a proper relationship. I'm guessing its because he's not with his popular friends now (they keep contact but are all moving to different universities), and he feels free-er bout dating people they might not accept.

But, I think I'm just leaning on Guy A since Guy C left. He was everything to me, and I still love him a lot. We didnt talk for a month and a half after the breakup, but he replied yesterday. Guy C is my longest relationship, and we were really serious about each other. He was insecure about my ex's and me being friends with other guys, but he also looked after me, and cared for me like no one else.

Whatt about guy D, E, F all the way through to Z then round the alphabet again AA, AB, AC etc?

As WazzWazz98 quite rightly and very wisely said there's a lot more guys than these 3 in the world.

Try to never settle for 2nd best. And also at the same time don't be perfectionist. Strike the right balance between selective enough and being too intolerant.
It helps a lot if you have an abundance of options. You've gotten 3 men interested in you so far. You'll be able to get more men interested in you in the future.
You will also find that there's a large difference in teenaged boys and men that have been through a few relationships. Teenaged boys tend to be poor boyfriends that just bring too much stress and drama into your life. Due to their lack of experience.

Guy C told me he's still talking to me now because I'm acting pathetic and he used to have something with me. It hurts. I know I dont want to date him again and I told him that, its just that sometimes I worry that all guys are like that, even the best ones find something wrong and then leave. You are right, i keep falling for boys and keep treating them for men. I've had more guys interested me and I've been picky before, I just want some one to lean on and listen to me, understand me, instead of having to be strong all the time.