Friend's Involvement in Plagiarism So, I've edited the question to hopefully give more clarity on the situation:

I've recently learned that my friend ( A ) assisted in plagiarism for another student ( B ) by completing the vast majority of a final-project in a class I also take with student B. I know B doesn't deserve the almost-perfect grade he will receive because of A's work. I feel terrible because I know how much effort I and others personally contributed to our own projects and it makes me feel like everyone else's work has just been invalidated.

I know, beyond any doubts, that this is what occurred:

B has struggled in this class. A is experienced with the class, the professor, and the subject matter. A has been helping B with other assignments, sometimes assisting more than he should, but otherwise not at any level I would deem "plagiarism."

B asked for help with the final project in this class. A, of course, obliged. After helping for a little bit, the due date was imminant and B's project was still in the beginning stages. At this point A realizes that he has basically been completing the project himself, but feels morally obligated to not "leave him stranded," so A fully completes B's project out of a personal, moral obligation to himself. Personally being friends with A, I know that this was a momentary lack of judgement, and I know he knows much better than to cheat.

A has done all of the work on the project and B is going to pass it off as his own work.

Looking at the College's plagiarism policy, the worst that will happen to the student B is:
 Failure in the course in which plagiarism or dishonesty occurs.

For my friend ( A ) that knowingly plagiarized: Loss of all credit for that semester and suspension for the remainder of that semester.

My friend A has struggled this whole semester, academically and financially, to attend the College and it would be horrific if he had to leave and all of his work be for naught. I find it also unfair that, for what A found as a moral crossroads (helping his friend), and a momentary lack in judgement, will cost him so much more than the punishment B will receive.

I want to report it, but if I do (even anonymously), B will only tell the administration that my friend helped him. I can't be responsible for that.

What can I do in this situation? Report it? Keep it to myself and hope the professor knows? Meet with the professor and have an honest discussion about how I feel and how I know my friend knows the ethics of cheating but became morally confused in this instance?

I guess the overarching question here would be: what outcome provides the best result for A while simultaneously reporting B for plagiarism?
I suggest a middle ground. Even granting that the facts are exactly as you stated, it seems to me that you don't know for sure what communication there was between A and B. A may have provided some sample code, intending that B would at least rewrite it. And, unlikely as it seems, B may have studied the code and rewritten it. So this could be a borderline case. Even if A complained to you that they had to "write B's assignment for them", that may have been an exaggeration.

So I suggest that you go to the professor and explain that you think that B had an excessive amount of help. Explain that someone was tutoring B, and may have crossed a line without intending to. I don't think you need to name A even if you are asked. And if the professor does find out who A is, well, professors are people too, and will probably exercise some judgement.

Of course, I'm not excusing what A or B did. I'm just pointing out that you don't know exactly what happened (even if you're sure you have the facts straight), so report what you know, but be careful not to overstate it.