You've never been one to scare easy but she terrifies you. You can't let them go without knowing because you've come to care about them. They're your friends and he's a time bomb. Going under would mean she would be there and that's a risk you can't let them take alone. He's taken precautions, sure, but is it enough? You sure as hell don't think so.
That's primarily because you can still remember when you created the bridge for him and she stabbed you. The pain was sharp and immediate, enough to make you wake up gasping for breath. But then there was the elevator and the memories. Your heart broke for him then because of all the pain he'd brought on himself. It was her fault. Part of you is angry that he'd risk all of them, but another part understands. You'll see him to the end of this and you'll help him find closure. That's more important than finishing the job as far as you're concerned. He's shown you a whole new world. It's the least you can do.