Edited 6/5/14 to add: Different professor, different department, but this is all going to get a lot worse before it gets better. What really struck me in the student's account was this: "Convert the professional relationship into a personal one. Establish trust and a close personal friendship with the person... He said that out of all his lovers, I was the fastest one to go to bed with him. He said it usually took him many months, even years, before young women went to bed with him." That is the pattern that makes this all so pernicious. The person I'm describing here has justified his bad behavior in past instances by blaming it on a general "twisted sexual culture" at yet another ancient university, all of which raises the classic chicken-egg question.
Don't do it.
I didn't listen to advice when I found myself in a similar position to yours and I don't expect that you will either, but don't do it. You're at a good moment, graduating from college, to make a clean break. I know that you have a place to do a Master's degree in a place that is familiar with faculty you know and adore, but don't stay. Work for a year and reapply to different programs next year if you still want to work toward another degree. But for now, in this one very fundamental way, put yourself ahead of your professional aspirations. Turn around, start running, and don't ever, ever look back. As hard as it may seem to leave what has become familiar and comfortable and desirable to you, it will never again be this easy to walk away.
He's young (compared with your other professors, anyway) and adorable and so terribly, charismatically charming. You are struggling with how to balance your own religious life and your academic work that touches up against it, and he seems to have that all figured out perfectly. He dotes on you. He knows how smart you are and how, with a little guidance, you'll outshine him one day. (This last bit is true: you will outshine him, but you don't need him for that.) You are even friendly with his wife, so it all seems perfectly safe. It is not safe. Run.
He will gaslight you and make you doubt grasp on reality. He will manipulate your time and your energy. He is so skilled in deception that you will believe the same lie again and again. This is a critical juncture, because if you continue down this path he will later point out that won't have made a move on you until after you'll have graduated — he'd never get involved with an undergraduate! — and you'll already be so twisted around that it'll seem noble.
I think that what he will tell you about having no sexual relationship with her is probably true, but after that it will all be varying degrees of lie. And that's just it. It's not about you, which makes it both easier and harder to take: Easier to take rejection when it will inevitably come, because it's not really about you. Harder to look back upon when you realize that a whole, intense, intimate relationship was never about who you were, but rather was about who you weren't. He doesn't value you for you, for the wonderful you whom he claims to adore for all her uniqueness, but rather he values you for being a non-her female entity.
The piece that I never realized until now, until I heard bits and pieces of your story is that she's in on it, too. I don't mean to make this sounds like a conspiracy. I'm sure they never sat down and had a conversation to set up a system; but befriending his young female students along with them, cooking with them, making them feel at ease in the situation, and then looking the other way as he does this over and over and over and over again, all of that must be her way of giving him what she herself cannot or will not.
He is a predator. He is grooming you.
Yes, you are an adult, if only just. Yes, you will consent to anything, emotional or physical, that you will do with him. But he will still be taking advantage of how young and stupid and starstruck you are; please understand that last remark sympathetically. I was that young and stupid once, too. It took the better part of a decade for the relationship to run its course and for me to finally be able to move on. I can tell you how to begin to fix yourself once it's all over. I can tell you how to start allowing men to treat you properly after the mind-and-heart-scramble you're about to take. But I don't have any practical advice for the better course of action, which is to get out of this before it's too late.
All I can say is this: Run.
Love and live-and-let-die,