Warning: Spoilers
(not vague ones!)
...and you believed them? That's downright shameful. It's as equally likely that the Shepard-Ghost will get corrupted, just as Illusive Man did. To think that one existence can control a force as insidious as the Reapers is the pinnacle of hubris, and you fell for it. Just watch it. You look like you're getting turned into a husk.
As for who you lose in choosing the Red ending, I've made plenty of sacrifices throughout the trilogy, ones that I certainly didn't want to do. What's one more group for the sake of trillions?
ME3 is an entire game of hard choices. I already had to let the Quarians all die for their aggressions, despite my best efforts. I replayed that whole section just to see what I had done wrong, couldn't change it. Sacrificing the Geth for everyone else wasn't that hard, because Legion was already dead. It's hard to sympathize with the other Geth. EDI was a regrettable loss, but this game showed us plenty of times that you can't save everyone.